Summary: Implemented Cadair's requests for issue #483.

The following changes were made in this commit -:
1. iris.py had a missing IRISMap class definition; added it from master.
2. All Map imports present in instr/<instrfolder>/<instrname>.py from last commit were shifted to map/__init__.py.
3. Map.register() calls were added to map/__init__.py.
4. py.test was run and an offending IRISMap import was removed from instr/iris/iris.py.