Handle more command line arguments

[Inei1]

Solves #26. There are three command line arguments in the PC facade that work with a headless server added by this PR. More testing is needed for the -overrideDefaultConfig argument, but the others work perfectly. Most of the new code is duplicated from the PC facade.

[gianluca-nitti]

Thanks - tested and works fine, also -overrideDefaultConfig. My quick test consisted in

• preparing this command line - through IntelliJ's "Program Arguments" field - -homedir=terasology-server -overrideDefaultConfig=override.cfg, the same as the default headless run configuration without -headless which is obvious for the server facade
• deleting the terasology-server directory to start from a clean environment, without config and old saves
• modifying override.cfg by adding "defaultSeed": "someTestSeed" to the "worldGeneration" section
• launching FacadeServer with the command line mentioned above
• waiting for it to save
• opening terasology-server/saves/New World/manifest.json, and as expected the "seed" entry was"someTestSeed" instead of the default "blockmania"

[gianluca-nitti]

Small GitHub tip: when a PR fixes an issue, like in this case, you can use one of the keywords, like fixes instead of solves, and when the PR is merged the issue is automagically closed :slightly_smiling_face: