Another small improvement

Related to 9313c1e6a97e435175646490dfd4c7c3a0c43863
Reorganize cms.db package

Provide imports from cms.db instead of cms.db.SQLAlchemyAll.

Use lowercase module names (as mandated in [1]).

[1] http://www.python.org/dev/peps/pep-0008/#package-and-module-names
Make imports from cms.db instead of cms.db.SQLAlchemyAll
Remove executable flag from some files
Fix drop_db

It failed with the following error when trying to unlink too many large
objects:

psycopg2.OperationalError: out of shared memory
HINT:  You might need to increase max_locks_per_transaction.
Update documentation
Improve cmsInitDB and cmsDropDB
AWS: fix (again) result cloning on new dataset creation
Some fixes to RWS