GURPS Sheet - Update 2

A large improvement on the previous pull request. Field sets now work, and the styling is improved (especially for the field set controls, which now blends with the sheet better). There are also a number of new tooltips for quick reference.

Most auto-calc is now working and implemented with the notable exceptions of Attributes and Skills, which are waiting on issue #165.

I'm sending a pull request so that others can contribute to this sheet if they desire without duplicating our work.