Update validation to match server error.

When a using the forgottenRoute if you enter an incorrectly formatted
email address you would see the error message 'Invalid Email', however
if you entered an email address that was correctly formatted but missing
the error message would be 'Invalid email address'.

This fixes the discrepancy.
Add User Role Dropdown

Closes #3402, Closes #3428

-------------------

 ### Components
- Added GhostSelectComponent to handle async select creation (h/t @rwjblue)
- Added GhostRolesSelector (extends GhostSelect) for displaying user role options
- Created StoreInjector for surgically inserting the store into things that normally wouldn't have them.

 ### Users Settings
- InviteNewUserModal now uses GhostRolesSelector & defaults to Author
- The role dropdown for user settings has permissions set per 3402

 ### User Model
- Added `role` property as an interface to getting and setting `roles`
- Refactored anything that set `roles` to set `role`
- isAdmin, isAuthor, isOwner and isEditor are all keyed off of `role` now

 ### Tests
- Added functional tests for Settings.Users
- updated settings.users and settings.users.user screens
- fix spacing on screens

 ### Server Fixtures
- Fixed owner fixture's roles
Merge pull request #3436 from novaugust/user-role-dropdown

User role dropdown
Implement user and related content deletion

Closes #3100

* Introduces `destroyByAuhor`, given a context and an id, it will check if context has permission to delete the user by the id, and then deletes all the content where `author_id` is id, and then deletes the user
* Does multiple checks to make sure user exists
* Added a fixture `posts:mu` that creates 4 users belonging to 4 roles, 50 posts that have authors evenly distributed, 5 tags and all 50 have one tag attached to it, evenly distributed.

Caveats / questions

* Started testing
Add keyboard navigation of posts

Closes #3015
- Added stepThroughPosts method to PostsRouter, takes a integer, goes that far, wraps around the array.
- PostsPostRoute notifies the PostsController of which model it currently has, to help stepThroughPosts know who's selected
Merge pull request #3470 from novaugust/up-down-posts

Add keyboard navigation of posts
Merge pull request #3467 from rwjblue/update-validation-to-match-server-error

Update validation to match server error.
Merge pull request #3371 from javorszky/iss3100

Implement user and related content deletion
User edit & add endpoints cleanup

- edit and add endpoints don't assume role
- edit and add endpoints cope with no role, role objects, and strings
- resend user invite was failing at one point due to no role being sent, but this shouldn't be required
- other random api cleanup