added test case for reconstruction and variant for the same voice
changed name of test file to standard Du Chemin name
test case with a single variant source
fixed parameters for test case DC0221
updated MEI test files that are generated by Sibelius plugin

revised passing test cases (marked TCs causing segfault)
adjusted a test case to test NCName correction
Convert Source IDs into valid NCName strings
Merge branch 'ncname'
ignore database file
fix ignore
merge <score> elements into main <staffDef>s
merge milestone scoreDef (the one after the first measure) back to main scoreDef

- some coding style consistency
- warning messages
don't add empty sourceDesc, titleStmt
updated DC test files

changed some test file names to standard DC names
Merge branch 'clefchange'
get_descendants() implemented in python

unit test file added (testing get_descendants() only at the moment)
using get_descendants() in incipit.py
use python get_descendants()
more source label conversion testing
Renamed Variant test '04' to '00'

previously segfaulting test cases now pass using a fixed libmei (see
https://github.com/DDMAL/libmei/commit/370fea8efb40eccc4fed3a55dcffbd72b
68efebb)