Minor Qf formula updates
replaced checkWff with isWff
added TF functionality to QfWff.g4 and added more tests to QfWffCheckerTest
Updated grammar to be closer to properly recursive
The Qf grammar is a mess at the moment... but it passes most of the tests
Started working on treewalking / treelistening
Created test for QfWffChecker.containsRedundantQuantifiers
QfWffChecker now only accepts Wffs without redundant quantifiers.
Minor refactor to make QffWffTreeListener more simple
Renamed WffCheckerListener to WffCheckerErrorListener