Move StructureResults to org.nlogo.compile.front.

- Extract common interface for procedures to api.FrontEndProcedure
- Remove nvm references from NameHandlers, Namer, StructureConverter, StructureParser
- Move backification marginally later in the compilation process
Merge pull request #17 from NetLogo/wip-mitosis-remove-nvm-deps

Move StructureResults to org.nlogo.compile.front.