Fix floaring header gradient in FF and settings images

No issue

- Corrects the syntax used for the floating header gradient so it now gets prefixed correctly for Firefox
- Removes padding from `<button>` elements (fixes padding around images in buttons)
- Adds display: block; to settings images to prevent a Webkit bug which adds space under the image
Merge pull request #3952 from PaulAdamDavis/fix-what-libsass-broke

Fix floating header gradient in FF and settings images
Don't send HTML on post save.

fixes #3956
- adjusts post serialiser to not send HTML content
Prevent editor title from being overwritten

Closes #3955
- Change titleScratch from being bound to the title to being
  set when entering the editor so it is not overwritten on a
  model refresh.
- Ensure that the "unsaved content" dialog is shown when there are
  changes to the "scratch" fields after a post-settings-menu change.
- Add tests to prevent regression.
Merge pull request #3957 from halfdan/3956-we-dont-like-html

Don't send HTML on post save.
Stop packagePath variable from being undefined
Adds (Never) for users who haven't been seen

Closes #3970
Remove form focus halo

No issue

- Removed the blue halo from around focused form elements
- Slightly refactored the forms to target less text inputs and have cleaner syntax
Merge pull request #3971 from javorszky/iss3970

Adds (Never) for users who haven't been seen
Merge pull request #3972 from PaulAdamDavis/form-refactor

Remove form focus halo
Merge pull request #3963 from jaswilli/issue-3955

Prevent editor title from being overwritten
Merge pull request #3968 from thaiphan/master

Stop packagePath variable from being undefined