Support Other Expression Languages

[geoffreywiseman]

Add support for one or more other expression languages like:

• OGNL
• Commons JEXL
• JUEL
• SPEL

etc.

This is basically only something I'll bother with if I or someone has a strong reason to use something other than MVEL and makes a good case for it. This will be a lot easier to do now that the mechanism for having a core module and an expression language extension is already in place, but it's still only worth doing if someone needs it. I don't, currently.