Move Glyphicons into their own repo

Removes the icon fonts and associated docs and LESS code from the core
repo and into twbs/bootstrap-glyphicons.
Merge branch '3.0.0-wip' into bs3_remove_icons

Conflicts:
	docs/components.html
remove icons from sidenav
delete icons in assets
remove glyphicons from demo component
add docs callout for glyphicons on homepage and CSS page
Merge pull request #8332 from twitter/bs3_remove_icons

BS3: Remove Glyphicons