Ensure incomplete tags aren't lost on save

closes #2991, references #2172, references #2453
- moved and separated tags logic from EditorTagsView into PostTagsInputController/View
- call out to PostTagsInputController when saving post to ensure an incomplete tag is completed before save
- added Tab key support for suggestion selection / tag completion
- don't show suggestions list when input field doesn't have focus
- added code for #2172 but left commented-out as it causes side effects with completion on save
- updated suggestion highlighting so it doesn't bork on html/regex chars (#2453)
Uncomment signin validation test + test cleanup

closes #2989

- classing this as finishing the casper tests for now
- adding a name to the description in the settings template
Merge pull request #3061 from ErisDS/issue-2989

Uncomment signin validation test + test cleanup
Merge pull request #3005 from kevinansfield/ensure-incomplete-tags-arent-lost

Ensure incomplete tags aren't lost on save
Prevent notifications from being too tall and unclosable

Closes #1558

- Adds a wrapping tag around the notification message
- Change tests to look for new wrapping tag

For the fix to work properly, it needs styles from the [0.8 branch](https://github.com/TryGhost/Ghost-UI/commit/b98029911c4695f17cb9d05bc48ca5e8eeb77bf6) of Ghost-UI