New Yesod.Form.Bootstrap3 module.

The original renderBootstrap code was heavily modified by
Mladen Srdic [1].  I took his code and modified it as well,
and the result is this commit.

[1] https://www.fpcomplete.com/user/msrdic/bootstrap-3-forms-with-yesod-1
Deprecate the original renderBootstrap.
Ignore backup files.
Bump yesod-form to version 1.3.8.
Smarter with{Small,Large}Input, do not override existing classes.
use fewer imports
parseJsonBody_ deprecated for requireJsonBody
add forkHandler. closes #680

Also fix import warnings in Handler
Merge pull request #689 from yesodweb/fork-handler2

add forkHandler. closes #680
Merge pull request #687 from meteficha/bootstrap3

New Yesod.Form.Bootstrap3 module
Add missing import
Use correct error classes on Bootstrap3 module.
Do not display FormFailures as they contain duplicates of field failures.