fixes #5102, #5166, #5194, #5205: add overflow: visible; to .nav-collapse.collapse so that dropdowns overflow correctly in the navbar in IE7-8

add new vars for common border-radius, upping border-radius of inputs to 4px; add border-radius changes to -large, -small, -mini for buttons and paginations

add new vars for common font-sizes and paddings with large, small, and mini components; resize pagination and buttons to better match each other

fixes #5177: remove color on .btn-large .caret, but keep sizing change; also start to add CSS tests for buttons

Add CONTRIBUTING.md

Signed-off-by: Chris Aniszczyk <zx@twitter.com>

fixes #5041: add new navbar css tests for each variation, remove width: 100%; from .navbar-static-top

Use @bodyBackground on .nav-tabs active state instead of static color

add in some more examples (will work em in later), removed fleetio per their request, and added gather content to replace it

mistakenly committed ALL assets. since only bootstrap.css and bootstrap.min.css are changed i removed all others