LESS tweaking

Hello @tessr, 

Please review the following commits I made in branch 'prezjordan-less-finagling'.

5b19bc71ba869d728a4ddc195124c6a691c0ae8d (2013-07-26 19:35:32 -0700)
pluralizing more LESS

b3f6c0be9bc35622011252c588c315292faa70db (2013-07-26 19:29:41 -0700)
Converted button.css to LESS - pluralized


R=@tessr