Read a configuration file with Hets's location

[eugenk]

The location of Hets should be configurable:

• URL to a Hets-server instance, e.g. http://localhost:8000 or http://rom:800
• local absolute path to a Hets executable

If a local path is configured, start and stop the Hets server locally similar to https://github.com/ConceptualBlending/conceptual_blending_project/blob/7c6014d3b4d7f461d668e039460bac1cefc58073/script/lib/conceptual_blending/hets_server.rb

Maybe allow to configure a port range for starting Hets locally.

The RabbitMQ server's location must be configurable as well.

Use the gem railsconfig/config for the config files to allow a config.yml, config.production.yml, config.development.yml, config.test.yml and config.local.yml (or similarly named).