Add base64 support to grunt file

This includes all images directly into the css files. I was not
able to get production working with the bower-gem and the
assets pipeline related to diaspora/jsxc#28
Fixes smiley-box icon behind hint text
Move image url into stylesheet in respect of assets pipeline
Try to build everything via travis
Merge pull request #44 from Zauberstuhl/add_base64_support

Add base64 support to grunt file