Update ghost-logo, death to jQuery

Amends #3740 (which amended #3736), ref #3623
- Removed futzy jquery for setting href on logo; binding to ApplicationView property
- Killed dead code
Error notification if send mail api returns 500

closes #3728
- If the mail config is broken, the ajax call will fail with 500 and
not return an error.
- This change catches 500 and wraps the error in a notification.
Fix and enable general and user settings tests.
Ensure editor awareness if publishing fails

closes #3667
- If the ‘save’ function on a new post fails, the local Ember model
still beliefs that the status is ‘published’, resulting in wrong
buttons. A simple catch fixes that.
Merge pull request #3773 from jaswilli/settings-tests

Fix and enable general and user settings tests.
Merge pull request #3749 from novaugust/ghost-logo-link

Update ghost-logo, amend the amdendments, death to jQuery
Merge pull request #3738 from felixrieseberg/iss3728

Error notification if send test mail returns 500
Merge pull request #3776 from felixrieseberg/iss3667

Ensure editor awareness if publishing fails