Merge pull request #1 from MapQuest/mla-group-symbolizer

Factored out placement checking
Create sub features and match them to group rules.
Add group layout manager
Parse placement properties for GroupSymbolizer. Fix white space in load_map.cpp
Add group layout manager
Added method to extract bounding boxes for symbolizers.

This is done by creating a fake 'virtual' environment at a fake
point and running the symbolizer render code. The actual render
is saved in a thunk for after the group layout has been done.