Support browser implied authentication
Refactor browser implied authentication

Put FAKE_IMPLIED_TOKEN on RemoteStorage.Authorize; remove GDrive/Db
code; fix tests The FAKE_IMPLIED_TOKEN variable was not available from
wireclient and sync; making it a property of RemoteStorage.Authorize
fixes that. Also, the code in googledrive.js and dropbox.js was useless,
as implied auth is not supported there anyway. Finally, some unit tests
were failing, and this is fixed by defining
RemoteStorage.Authorize.FAKE_IMPLIED_TOKEN in their setup
Add changelog entry for browser implied authentication
Merge branch 'feature/602-implied_auth'