Replacing Location object with GroundStation object (in progress).

* Refactored component names to org.hbird.exchange.core.constants.StandardComponents.java
* Refactored argument names to org.hbird.exchange.core.constants.StandardArguments.java
* Added methods getSatelliteByName and getGroundStationByName to ICatalogue.
* Added getters and setters to CommandArgument.
* Refactored argument creation in Command and it's sub classes.
* Refactored argument handling in Command class.
* Added some unit tests.
* Added mockito to dependencies.
* Lots of additional refactoring.
* Replacing Location object with GroundStation still in progress.