Version 3.23 released

Catching all exceptions and casting them to messages rather than sending them to console
Removed the annotation index (first of two numbers) from the drop-down list
Modified the context window to add an indication if an utterance doesn't have SRL
 - Created a context-to-annotation map that can be used later on
 Added '=' as a shortcut for predicate
 Added list of commonly used shortcuts in the F1 menu
 Added a bracket-verification method during tree editing