cleanup function to sanitize protein structures

modules/conop/doc/cleanup.rst

modules/conop/doc/conop.rst

modules/conop/pymod/CMakeLists.txt

modules/conop/pymod/cleanup.py

modules/conop/tests/CMakeLists.txt

modules/conop/tests/sample_noligands.pdb

modules/conop/tests/sample_nowater.pdb

modules/conop/tests/sample_test_cleanup.pdb

modules/conop/tests/test_cleanup.py

modules/mol/base/pymod/export_residue.cc