Added ability to stop too many feats being added

Added a check every time user attempts to add a new feat or class
feature to their list. If the new feat or class feature wouldn't fit on
their character sheet an error dialog is created.
Added support for different sheet types

The program checks the ClassAndLevel element and changes the maximum
feats and class features allowed accordingly. The pdf formats the
element strangely however (it adds in formatting information) which
makes it hard to read. I'll see if I can fix the pdf so it doesn't
format the element.

Also changed a couple of comments that didn't make sense.