Use pkg_resources to access migrations files. When dexbot is packaged
into egg file (normal `setup.py install` result), we cannot just access
files inside egg (zip archive), so we're using native setuptools API to
extract the files (resource_filename()). In case files are not in egg,
pkg_resources will use normal file access.

https://setuptools.readthedocs.io/en/latest/pkg_resources.html#basic-resource-access
https://setuptools.readthedocs.io/en/latest/setuptools.html#accessing-data-files-at-runtime
http://peak.telecommunity.com/DevCenter/PythonEggs#accessing-package-resources