Merge branch '2.1.0-wip' of https://github.com/nextgenthemes/bootstrap into nextgenthemes-2.1.0-wip

Conflicts:
	less/buttons.less
fixes #4027: same margins on .pager and .pagination
fixes #3973: same border on disabled inputs as default inputs:
Merge pull request #3937 from codler/patch-4

Update linear-gradient standard
update comments after merging gradient change
fixes #3384: add support for multiple inputs per line when using grid sizing
fixes #3381: update docs to show correct media query range on responsive utilities
fixes #3210: add .btn to .navbar-form to remove bottom margin, improve vertical align of contents of .navbar-form
fixes #3291: remove float on responsive .thumbnails for 767px and down to ensure thumbnail images don't pop out of container in FF
fix up docs popover examples and copy
remove popoverarrows mixin, relegate code to tooltips and popvers since we only used them once each; this fixes the problem of broken tooltips in 2.1
update Extend docs page to include side nav and spec out next section for extending with static assets
fix indenting on extend and js docs pages, remove hidden subnavs
fix indenting and remove hidden subnav on Base CSS docs
fix indenting and remove hidden subnav on Scaffolding
fix indenting and remove hidden subnav on Components
Fixes #4002 responsive utilities classes
fixes #3605: add support for input-prepend/-append to .form-search
add vars for tooltip customization via background and color
fixes #3706: add textColor and textShadow as options to .buttonBackground mixin