Some variables movement.

Moved variables from code, dropdown, forms, input groups, jumbotron, labels, navbar, panels, popovers, thumbnails and type to variables.less and customize.html

@cvrebert I am seeing "browserstack_runner" errors and its causing Travis CI build errors, can you please let me know why its happening so I can fix or you know why and just ignore it and merge my changes.

@mdo I have tried to be careful this time tried to avoid any unwanted errors. Tested and built locally works fine.

Just got confused, I am seeing wells.less file back and its variables as well. Aren't it supposed to be replaced with jumbotron?