UX improvements

[jmartsch]

Please integrate the following UX improvements into the core.
Some of them could be optional like the sticky header. But I think most would make sense for everyone.
Most of them are taken from AdminOnSteroids:

• CTRL-S hotkey to save a page
• live filter (find as you type) for asmSelect fields, AdminDataTables, modules
• add field and template edit links (at least for superusers)
• add a download button for file fields
• don't truncate filenames in file fields
• Show save dropdown on hover instead on click
• Add sequential tabindex to fields
• Add links to edit previous and next pages (very useful)
• Sticky header in AdminThemeUIkit
• Improvements for pagelist
  • Highlights on hover
  • Add pagelist Delete action and page edit checkbox to bypass Trash (SuperUser only)

[BernhardBaumrock]

:)

[adrianbj]

In keeping with the theme of AOS features that I think are really needed in the core are these:

• A sidebar for the page edit interface (ie the AOS column break feature). This is absolutely essential for me.
• Add button to check/uncheck all checkboxes (appears on hover)
• Add unselect/restore buttons to PageListSelect
• Show pagelist actions on full row hover

@ryancramerdesign - would you be amenable to PRs for the AOS features that we all use (and honestly really need - many are very hard to get by without).