Moved all parser messages to a properties file and improved many of them.
Made Association limiters like braces so that the matching counter part is highlighted .
Slots are no symbols anymore but they are highlighted when in context of a anonymous function
Separated association slots #foo from others and gave them a separate AST element type
 MessageName PsiElements can now return their symbol, tag and language
 Split parsing of Slots from parsing of symbols
 Improved smart completion when inside Message[..]