Improving test_note_rest_indexer.py

- Two tests for Indexer._do_multiprocessing() with mock MPControllers
- One test for same with real MPController
- Both adjusted to use minor changes to MPController forthcoming
Improved test_indexer.py

Added a test for de-pickling things.
Adjust Indexers and Their Tests for the MPController

- Indexer._do_multiprocessing() pickles Score objects
- indexer.mpi_indexer() unpickles Score objects
- IntervalIndexer heeds settings (untested)
- NoteRestIndexer works with MPC
- Updated TemplateIndexer
- Add IntervalIndexer test with real MPC
MPController Slightly Optimized; now Has Some Tests

... but by optimized I mean "optimized" and by tests I mean "tests"...