PR that adds selectables to metafora.  Uses QLBridge for selector parsing. 

@araddon : Here is the QLBridge code.   

I could use your input on how to deal with array variables.   For example how to do a `contains` on a set of values.  
For example if the selector is `contains(allowed_accounts,"123")`,  I would like it to search allowed_accounts for exact matches...