Fixes to setup.py and cbc.py
setup.py: add "bin/manifold_cbc_bank_constrain.py" to scripts; manifold/sources/cbc.py: add try/except to fix logsumexp import error
setup.py: add "bin/manifold_cbc_bank_constrain.py" to scripts; manifold/sources/cbc.py: add try/except to fix logsumexp import error