Additional data element for worship song list. Tempo Category.

I started out today adding a tempo type field for all elements, but after it was completed, and even live for an hour or two, I decided to change it to be a 'custom category' field.

So, you can create your own categories in the settings page, like 'fast', 'slow', 'favourite,' 'song book', and add songs that are in your repertoire to one category.

It would be nicer if there were multiple categories open to each element, but for now this should prove to be a useful feature.