Added /roles/ API endpoint

[javorszky]

Closes #3196

• adds /roles/ endpoint, currently there are no other parameters to pass
• gets the current user as context
• filters available roles according to current user's roles' and only returns the ones that the current user would have permission to assign
• if we're not signed in, gives a "please sign in" (standard) error
• if we're signed in, but user is not in the context, gives a "there was no user in the context" error
• if the user is an "Author", gives a "there are no available roles to assign" error

Caveats:

• hacky implementation of the filter, at some point it should be solved with canThis
• there are no tests
• for some reason the setup functional test was failing for me locally

[javorszky]

I'll put in tests once tests actually run again. Currently they fail on a tag after each hook, and then on a casperjs POST to /token/.

[javorszky]

@ErisDS, wrapped the call in a canthis browse

[javorszky]

Yup, the mysterious tag.aftereachmodel thing. Once that's solved I think I'll have to rebase and have the test run again. I'll look at those tomorrow.

[jaswilli]

filters available roles according to current user's roles' and only returns the ones that the current user would have permission to assign

@javorszky I know there aren't actual tests for this behavior, but did you confirm that this part of it was working?

I'm going through #3083 and when I make a call to /ghost/api/v0.1/roles/?permissions=assign I get no results back for any user other than the owner user (id: 1).

[javorszky]

@jaswilli, hm... it should work. I'll test it though, and will write tests for this (hopefully it's going to be easy-ish)

Thanks for flagging it up!