Add JSXCS pre-commit hook

JSXCS is a wrapper around JSCS for JSX files. As a result, adding this
was a simply copy, paste, and replace "jscs" with "jsxcs".

Change-Id: I192d7a109f0f3439ddb2c2ab4fe4ee7d0e0a1576
Reviewed-on: http://gerrit.causes.com/44154
Reviewed-by: Joe Lencioni <joe.lencioni@brigade.com>
Tested-by: jenkins <jenkins@causes.com>