support for more configuration files in Service.py, fixes #139

[jachym]

Overview

This patch adds support for more than one configuration files in PyPWS Service #139

Related topic

pywps-demo PR geopython/pywps-flask#11

(as per https://github.com/geopython/pywps/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to PyWPS. I confirm that my contributions to PyWPS will be compatible with the PyWPS license guidelines at the time of contribution.
• I have already previously agreed to the PyWPS Contributions and Licensing Guidelines