Code Refactor - Activation of environments

[DonJayamanne]

I leave the design upto @d3r3kk

Requirements:

• Move the classes and interfaces into an area related to Interpreters.
• Support multiple shells
• Support multiple OS
• Configure priority for activation providers/services (stratergy classes).
  E.g. First check env is conda, then activate using conda activation mechanism,
  Then we might need to try pipenv, and then virtual env, etc.
  Note: If one fails, we need to try others (i.e. priority queue).
• Support a fallback mechanism.
  E.g. if activating from powershell isn't possible but command prompt is, then we can go into CMD and activate as though it was a command prompt.

Testing requirements

• Propose/implement alternative testing techniques sinon, ts-mokito.
  Here is a great resource - https://medium.com/welldone-software/an-overview-of-javascript-testing-in-2018-f68950900bc3

[DonJayamanne]

Closing as all required features/changes have since been implemented.