make protected_path configurable, by default /ows/proxy

[fderue]

Changes

• The proxy protected path, previously hard coded "/ows/proxy" is now configurable in the settings as
  "ows-proxy-protected-path".
• Parsing of service_name in utils.py is now adapted to protected_path length

[cehbrecht]

Tests are failing because they have no registry.settings. You need to modify the tests. Hope this helps:
https://docs.pylonsproject.org/projects/pyramid/en/latest/api/testing.html#testing-module

twitcher/twitcher/tests/functional/common.py

Line 8 in e2380b7

def setup_with_mongodb():

[cehbrecht]

@fderue still something goes wrong in the tests ... haven't figured out. You can try the tests locally:

$ make test
$ make testall    # I think service needs to be started for this with "make start"
$ make pep8

[cehbrecht]

@fderue
looks good ... merged :)