Split unit_tests.py into unit_tests and unit_test_lib

Change-Id: Ia26fe26e65e251e4a06a1f0c733eba9d81392abb
Add function to apply time_signature to piece

Change-Id: Iba0266bdb6bc20bd863fc48257f55ee6797640c8
Just committing some experiments

Change-Id: Ie3d3791e7d32ef44aec854c6f721ce7c4b88fcdf