[Feature] Configurable Icon Class

While trying to use Font Awesome instead of the Glyphicons, I discovered the basic class for all icons was hardcoded to `glyphicon`. So I added another option in the config so this can be adjusted to whatever is suitable.

This is also helpful for anyone trying to use a custom build of Bootstrap where they have changed the class name.

Oh, and there was a minor case of double quotes being used where they didn't need to be.