Support other languages

• Event-B
  • Allow to load Event-B files (.eventb or possibly .buc)
  • Possibly allow Event-B syntax/parser to be used for formulas/expressions
• TLA+: allowing to type in expressions/predicates in TLA+ syntax (and call TLA parser); this feature is not yet available in probcli/ProB
• Z
• CSP
• XTL Prolog files