ignore intellij files
allow non-typesafe Lookup Refs in the id position of tx data

Lookup Refs are can be used as final ids in in
retractions, excisions and fetch by entity id

Desc of lookup refs:
http://blog.datomic.com/2014/02/datomic-lookup-refs.html
LookupRef's value type bound by the attribute type
Merge pull request #103 from rjsvaljean/topic/lookup-ref

Support Lookup Refs in Datomisca