cleanup entry points

This change cleans up our current entry points by:

* removing the development entrypoint `pyfarm-dev-dbdata` which is unmaintained and broken (due to missing imports) in its current state
* consolidating the `pyfarm.master.entrypoints` package into a single file
* adding a `pyfarm-create-tables` entrypoint which can be used to manually create all tables (it's currently needed by the agent tests)