Allow importing environment variables via Postman environment json files

[sboulema]

When importing a JSON file during the environment import we check for the Postman specific field _postman_variable_scope which should be set to environment.

If so, we re-format the JSON to the Postwoman structure and call the existing import function.
If not, we assume it is a Postwoman file and import it as usual.

This PR intends to add the feature discussed in #759

[TravisBuddy]

Hey @sboulema,
Your changes look good to me!

View build log

TravisBuddy Request Identifier: f20c0fa0-9368-11ea-84cf-61c3ab5f248b

[TravisBuddy]

Hey @sboulema,
Your changes look good to me!

View build log

TravisBuddy Request Identifier: f8fc0810-9368-11ea-84cf-61c3ab5f248b

[liyasthomas]

@sboulema Welcome to Postwoman collaborators team 💚
You've now earned much more control over PW repo. You can review PRs, assign issues, create branches and other perks of a collaborator. Pinky promise that you merge a PR with at least one accepted review from any of the collaborators. If you agree, kindly accept the invitation here: https://github.com/liyasthomas/postwoman/invitations

We've a Telegram group and Discord server to discuss about the project. Find its link from readme. Ping me for any doubts.

[liyasthomas]

LGTM 🚀

[sboulema]

Thanks for the invitation! Accepted of course, proud to be a part of the team 😄

[liyasthomas]

@all-contributors please add @sboulema for code

[allcontributors]

@liyasthomas

I've put up a pull request to add @sboulema! 🎉