Get module version according to PEP396

* Current implementation of get_version_from_app fails to get version
  information from modules such as numpy, webassets and setuptools since
  they define version information in the variable <package>.__version__
  and also include a module <package>.version. In the current
  implementation <package>.version takes precedence over
  <package>.__version__ thus the version information reported is a module
  instead of version number. This is easily fixed by this commit which
  changes precedence (see also PEP396).
Merge pull request #452 from lnielsen-cern/version_info_presedence

Fix module version detection