Added post invalidation

Posts are invalid if they are edited so I added three simple functions
to detect and apply flair if the submission was valid.
Updated README

Moved edited proposals to a "done" state.
Fixed condition

Invalid means *not* valid. Duh.
Reworked conditions

Made the functions a little clearer
Simplified is_ballot_valid code

I can do true/false code. Seriously.
Increased the get limit when checking in.
Merge branch 'master' of https://github.com/BrettWitty/ThenomicaBot into prop-invalidation
Made some minor style changes.