Installed jQuery.datetimepicker

https://github.com/xdan/datetimepicker/commit/3e320c9046f9c735bbff1c9e39056f
Swapped out jQueryUI datetimepicker for xdsoft datetimepicker
Removed jQueryUI datetimepicker
Added seconds to timepicker. Added masks to all datetime pickers
Fixed a couple of references to "localize" templatetags library
This was removed in 99a70b3
Merge branch 'master' into pr/286
styled datepicker nicer
Added I18N to new datetime picker
Aesthetic improvements to preview experience. Loading spinner now uses wagtail's standard glyph.
improvements from kaedroho feedback
tweaked transition
removed redundant script block
typo in comment
Merge branch 'master' into feature/minor-preview-improvement
move preview css to scss file
Only allow logged in users to access the userbar views
Raise exception if userbar views are accessed by anonymous user
Merge pull request #315 from davecranwell/feature/minor-preview-improvement

Aesthetic improvements to preview experience.
Merge pull request #286 from kaedroho/new-datetime-picker

New datetime picker