Easier integration of own index into Docker container

[MichaelRoeder]

Description

As a user, I would like to be able to use the Palmetto Docker image together with my own index (see #16). This should be made as easy as possible.

Tasks

• [ ] Move the properties file from the resources into a different place were it can be changed, easily
• [ ] Create two Docker images.
  1. A base image that contains the functionality and
  2. a second "standalone" image that contains the "default" index.
• [ ] The base image should be based on the latest tomcat 8 image (see #16).
• [ ] The description in the wiki should be updated accordingly.

[MichaelRoeder]

This has been solved by preferring environmental variables over the parameters defined in the "default" properties file that comes with the war-archive.