Added all post-function icon sprites to the app.
Remove FA icon from the form and used bg sprite for upload button.
Will match all other post / composer / widget ui buttons eventually.
Created a png sprite sized @2x based on largest usage (for retina).
This will fix some rendering issues caused by using svg images.
It will allow adding depth and more color / shading if we choose later.
mgabdev
Dank Gabs
robcolbert