Fix for multiple triggers toggling different classes on single targets

An issue was found which prevented multiple distinct triggers
toggling different classes on a single target. As an example, two
links that were toggling .class-a and .class-b respectively on a
single target element would only have toggled the class set by the
first trigger to run.

This commit rewrites a significant portion of the plugin so that
multiple triggers can toggle different classes on the same target.
Merge pull request #9 from abitgone/fix/classtoggle-multiple-triggers-single-target

Fix for multiple triggers toggling different classes on single targets