add stub v3 => v4 migration docs page

rename .previous => .pager-prev , .next => .pager-next

rename .item => .carousel-item

Move stuff out of configBridge.json now that the Customizer is kaput

remove remaining remnants of the Customizer

Remove docs notes about old Firefoxes

Remove defunct `background-image: none` Firefox-on-Android workaround

Remove defunct OS X Chrome <select> printing bug workaround

Remove ancillary references to IE<9 in comments+docs

Chrome fixed the bug as of v37:
https://code.google.com/p/chromium/issues/detail?id=282918

update Android comments in sauce_browsers.yml

Mozilla fixed the bug circa Firefox 33-35:
    https://bugzilla.mozilla.org/show_bug.cgi?id=763671
Firefox 34 is the current version.
Firefox 35 should be current by the time Bootstrap v4 is released.

remove IE8 from Sauce tests

bump min Firefox in Autoprefixer config to v31 (latest ESR)

bump min IE in Autoprefixer config to v9

Remove IE8 compat shims from JS visual tests

Add sache.json

Remove IE8 compatibility option from cssmin Grunt task config

Refs https://github.com/twbs/bootstrap-sass/issues/657

Use grid classes or mixins on .dl-horizontal, update docs to include it, removes auto truncate and makes .text-overflow mixin into a .text-truncate class and mixin combo for better granularity