MapGen: Support major version changes

[Katharsas]

This is the first task that needs to be implemented in the client to complete proper argument handling for the map generator as described here: FAForever/Neroxis-Map-Generator#35

Basically, when the client

• needs to know which map gen version it fully supports (example: client supports mapgen 1.8)
• needs to check the major version number of the map name when doing anything with a give map name (like when joining existing mapgen game or starting replay of a mapgen game), for example lets say user tries to replay a game of mapgen version 2.0
• if the major version differs (which is the case in this example), the client refuses to do the operation and tells the user that the client is not compatible and the user should probably update his client.

When this is in completed, new format for mapgen options can be introduced in mapgen 2.x like described in the mapgen issue.

Edit: Maybe a project should be created to include all related issues.