Agios 237

[corinnekrych]

This PR is an initial OAuth2 example (Shoot) which does OAuth2 authz with GoogleDrive and Facebook.
It does not do the actual upload as we're missing AGIOS-229, but @cvasilak you've got all the ground to test multipart upload with this initial version.

To test on Google no configuration required. To test on Facebook some configuration is required as fb required client_secret we can't commit config sample.

[corinnekrych]

@cvasilak @danbev do you mind reviewing it?

[danbev]

@corinnekrych absolutely

[corinnekrych]

@cvasilak please rebase as I've just added new http, oauth2 modules + shoot demo with acount manager for AGIOS-253

As we're working on closely related subjets, this branch is a WIP, waiting for @cvasilak to propose PRs. cc @danbev it may be wise to wait a bit for the review.

[danbev]

Tested Shoot and it works like a charm!
👍 On merging after the above comments have been addressed (the import one being option as @corinnekrych told be these will be used in the near future when Cocoapods are available for Swift)

[cvasilak]

👍 to merge, per discussion am in the process of creating separate Jiras for my comments so that we don't overcommit this PR