Remove Unused Files from Test Corpus

- update test_corpus/__init__.py
- remove difficult-to-use ABC file
- remove PDF verification cop-out for now-missing functionality
- remove regression tests for non-existent methods
Add BWV 2 to Test Corpus

We'll be using this file for integration testing, thanks to Prof. Rusch.
Add Tests for indexed_piece._find_part_names() and _piece_title()

Also some revisions to _find_part_names() so it works with some apparent
changes in music21's MIDI importing.
Revise .gitignore

- remove OutputLilyPond (if we use it again, it'll be a git submodule)
- add *.komodoproject for Komodo IDE files
Added "letter_to_relicense" in Preparation of Relicensing to AGPL