Implemented error messages

The main proof throws an exception with the user error message.
Justification display now uses JLatexMath
Increase font size of user input
Implemented subscripts for constants, predicates and propositions

Modifided parser to only accept id that are characters followed by digits
Error message for invalid parsing

iPandora will not perform no error recovery when parsing
Improve GUI

Increase font sizes
Increase icon widths so formulas dont appear across multiple lines
Fix repeat display bug
Added tabs to allow for multiple proofs

Refactored Gui code