Implement initial Drone CI for this KRSv2 project.

Add the following support in .drone.yml:
1) Support for both node versions 10 and 6.
2) Support for npm audit.
3) Support for eslint.

JIRA: BG-18745

Author: james8nguyen

.drone.yml

@@ -0,0 +1,100 @@
+---
+kind: pipeline
+name: check requisites (node:10)
+
+platform:
+  os: linux
+  arch: amd64
+
+steps:
+- name: build information
+  image: node:10
+  commands:
+  - node --version
+  - npm --version
+  - git --version
+
+- name: install
+  image: node:10
+  commands:
+  - npm install
+
+- name: audit
+  image: node:10
+  commands:
+  - npm audit
+
+- name: lint
+  image: node:10
+  commands:
+  - npm run lint
+
+---
+kind: pipeline
+name: unit tests (node:6)
+
+platform:
+  os: linux
+  arch: amd64
+
+steps:
+- name: build information
+  image: node:6
+  commands:
+  - node --version
+  - npm --version
+  - git --version
+
+- name: install
+  image: node:6
+  commands:
+  - npm install
+
+- name: unit-test
+  image: node:6
+  commands:
+  - npm run test
+
+trigger:
+  branch:
+    exclude:
+    - prod/production
+
+services:
+  mongo:
+    image: mongo:3.4
+
+---
+kind: pipeline
+name: unit tests (node:10)
+
+platform:
+  os: linux
+  arch: amd64
+
+steps:
+- name: build information
+  image: node:10
+  commands:
+  - node --version
+  - npm --version
+  - git --version
+
+- name: install
+  image: node:10
+  commands:
+  - npm install
+
+- name: unit-test
+  image: node:10
+  commands:
+  - npm run test
+
+trigger:
+  branch:
+    exclude:
+    - prod/production
+
+services:
+  mongo:
+    image: mongo:3.4

.eslintrc.json

@@ -0,0 +1,69 @@
+{
+  "env": {
+    "browser": true,
+    "es6": true,
+    "node": true,
+    "mocha": true
+  },
+  "globals": {
+    "app": true,        // BitGo side-effect from testutil
+    "ethUtil": true,    // BitGo side-effect from testutil
+    "requireCommon": true
+  },
+  "extends": "eslint:recommended",
+  "parserOptions": {
+    "ecmaVersion": 6
+  },
+  "rules": {
+    "operator-linebreak": ["error", "before"],
+    "max-len": ["error", { "code": 120 } ],
+    "indent": ["error", 2, {"SwitchCase": 1, "MemberExpression": "off"}],
+    "linebreak-style": ["error", "unix"],
+    "semi": ["error", "always"],
+    "eqeqeq": ["error", "always"],
+    "curly": "error",
+    "no-extra-boolean-cast": "off",
+    "no-unused-vars": ["error", {"vars": "all", "args": "none"}],
+    "object-curly-spacing": ["error", "always", {"objectsInObjects": true, "arraysInObjects": true}],
+    "array-bracket-spacing": ["error", "never"],
+    "require-yield": "off",
+    "func-call-spacing": ["error", "never"],
+    "quotes": ["error", "single", { "avoidEscape": true, "allowTemplateLiterals": true }],
+    "key-spacing": ["error", { "beforeColon": false, "afterColon": true, "mode": "strict" }],
+    "quote-props": ["error", "as-needed"],
+    "no-console": "off",
+    "no-empty": ["error", { "allowEmptyCatch": false }],
+    "no-inner-declarations": "off",
+    "no-useless-escape": "off",
+    "func-names": "off",
+    "generator-star-spacing": ["error", {"before": true, "after": false}],
+    "yield-star-spacing": ["error", {"before": true, "after": false}],
+    "no-duplicate-imports": "error",  // whilst imports are not being used, if we start to use them, we do not want duplicates
+    "no-unreachable": "error",
+    "no-path-concat": "off",
+    "no-process-env": "off",
+    "no-process-exit": "off",
+    "no-sync": "warn",
+    "brace-style": ["error", "1tbs", { "allowSingleLine": true }],
+    "eol-last": "error",
+    "no-trailing-spaces": ["error", { "skipBlankLines": true, "ignoreComments": true }],
+    "no-unneeded-ternary": "error",
+    "switch-colon-spacing": ["error", {"before": false, "after": true}],
+    "arrow-spacing": ["error", { "before": true, "after": true }],
+    "no-dupe-args": "error",
+    "no-undef": "error",
+    "no-var": "error",
+    "prefer-const": "error",
+    "no-compare-neg-zero": "error",
+    "no-extra-semi": "error",
+    "radix": "error",
+    "comma-spacing": ["error", { "before": false, "after": true }],
+    "comma-dangle": ["error", "never"],
+    "no-multi-spaces": ["error", {"ignoreEOLComments": true}],
+    "keyword-spacing": ["error"],
+    "space-before-blocks": ["error"],
+    "space-infix-ops": ["error"],
+    "spaced-comment": ["error", "always"],
+    "no-multiple-empty-lines": ["error", { "max": 2, "maxEOF": 1 }]
+  }
+}