pattern matching: split out Implicators to own file.

The number of implicators is multiplying. This needs some kind of simplification.
pattern match: move code around some more
pattern match: more code movement.
Pattern match: more refactoring
pattern match: more code movement
pattern match: whoops, typo in previous checkin
pattern matcher: change/simplify the bindlink API
pattern match: use temp atomspace for virtual atoms.
Merge pull request #1010 from linas/patty

Pattern matcher: general cleanup and code movement