make strings localizable (#888)

* make strings localizable

* fix: format errors using prettier

* fix: eslint quotes error

* fix: eslint quotes error

* pass TranslationBundle instead of ITranslator

* correct linter errors

* fix linting

* use nullTranslator for test files

* Update FileItem.spec.tsx

* use correct syntax in strings for translationBundle

* fix: parameter order in commands.spec.tsx addCommands(..)

* add suggested changes

Author: JessicaBarh

package.json

@@ -73,6 +73,7 @@
     "outputDir": "jupyterlab_git/labextension"
   },
   "dependencies": {
+    "@jupyterlab/translation": "^3.0.0",
     "@jupyterlab/application": "^3.0.0",
     "@jupyterlab/apputils": "^3.0.0",
     "@jupyterlab/codemirror": "^3.0.0",