Made Lengow environment-urls configurable

[berwa]

As we are not able to change our code depending on the target system (Magento production- or test-server) we can not use different Lengow-modules for the different Lengow-environments.
In this change we implemented a Magento configuration that allows the selection of the Lengow environment (Pre-Prod or Prod).
(Resolves #3)

[thedotwriter]

Thanks for working on this, I hope this PR won't get ignored. This is a feature that should have been included a long time ago.

[FredericMartinez]

PR still not merge, soooo, here a small repo with Plugins & Preference to handle environment via store configuration: https://github.com/PH2M/lengow-made-environment-urls-configurable

Enjoy.

[gthomas-lengow]

in production