added Bootstrap 3 support and some options

Now it can add the button before the input, create button and input container when class are set, and can create Bootstrap input group.
some bugs fixed
Update bootstrap-filestyle.js
Cerrected - Cancel on open file dialog issue #47
Merge pull request #46 from Aharito/master

Fix little CSS issue with required input attribute
Update bootstrap-filestyle.js
Merge pull request #1 from markusslima/master

Update to last
Merge pull request #2 from 85lele/patch-2

Patch 2