Fix #843: Ensure ColumnReorder styles override dijit themes
Fix #807: ColumnHider: Add aria-label to popup trigger node
Fix #852: Pagination: Add aria-label to rows-per-page select
ColumnSet: Reorganize scroller nodes to fix issues in autoheight grids

All scrollers are now placed in a single dgrid-column-scroller-container node,
allowing us to not lean on absolute positioning in cases of autoheight grids.
This in turn allows the scroller region to occupy space as necessary in those
cases, rather than obfuscating the last row of data.
Keyboard: Fix a checkbox/radio editor a11y regression; refs #893
Fix #760: ColumnResizer: Use smarter query for header cells

This obsoletes the prior filtering logic completely, which broke in
cases where custom IDs were used.
Merge branch 'master' into dev-0.4

Conflicts:
	extensions/Pagination.js