Fixup signin and signout

No Issue
- Move authentication related handlers to the Application route.
- Switch Sign Out from a button to a link.  Use the signout route
  to handle invalidating the session and redirecting instead of
  an action from a button.
- Clear error messages on signin page when pressing log in button.
- Errors are now always shown on sign in screen and a success
  notification is shown after sign out.
- Update functional tests.
Ghost instance not needed in update check test

Refs #3424, Refs #3444
- API and test suite refactoring triggered a conflict with
  the way update_check_spec.js was written.  Using a running
  copy of Ghost is no longer needed in those tests so it
  was removed.
Animations
Merge base.scss into global.scss
Buttons
Forms
Floating header
Deprecate old files and introduce _shame.scss

- New _shame.scss to hold styles/components which need to be refactored or removed
- layout.scss and floatingheader.scss merged into global.scss/shame.scss
Modals
Deprecate navs.scss, merge into shame.scss
Notifications
NProgress
Users
Merged rolelabels.scss into users.scss
Tables
Merged typography.scss into global.scss
No underlines
Uploader
Deprecate utilities.scss
Cleanup screen.scss / import uploader