AuthData logic refactor

[flovilmart]

• refactors OAuth to include anonymous as it's the same logic.
• Refactors the call logic to make sure all paths are consistent and no early return is send
• Refactors oauth/index.js into authDataManager/index.js to abstract validation loading + custom modules loading
• Adds support when the authData hash has more than one provider embedded (and according tests), when multiple linking occur one after the other
• Moves _auth_data_provider transformation to transform.js on update/create operations to declutter RestWrite
• Ensures authData is properly set and unchanged on beforeSave/afterSave _User

fixes #880
fixes #934
fixes #755

[codecov-io]

Current coverage is 91.61%

Merging #952 into master will increase coverage by +0.16% as of 74c0c22

@@            master    #952   diff @@
======================================
  Files           73      73       
  Stmts         4398    4423    +25
  Branches       880     887     +7
  Methods          0       0       
======================================
+ Hit           4022    4052    +30
  Partial         10      10       
+ Missed         366     361     -5

Review entire Coverage Diff as of 74c0c22

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@flovilmart updated the pull request.

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@flovilmart updated the pull request.

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@flovilmart updated the pull request.

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@flovilmart updated the pull request.

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@flovilmart updated the pull request.

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@flovilmart updated the pull request.