Display sources used as option for existing characters in select sources screen

Given PCGen is processor intensive, it's useful to pare back any loaded sources associated with a character so that it only loads with those sources essential to already chosen skills/traits/spells, etc. The large number of sources available means that it's not always easy to identify where different abilities originated. Having an option to display which sources a loaded character is pulling data from would help users to easily see which sources they can safely remove from the character.