Tested and nothing is broken. No major grumbles about the code. Some comments:
It's difficult to know if colonisation actually worked, so either a Toast or a Logcat entry would have been nice.
I don't understand why some methods take in a Sector array while others take in a GlobalGameData object. It appears inconsistent. Are there reasons to pick GlobalGameData over the Sector array? It seems like the methods don't use any other fields of the GlobalGameData.
Systems can be colonised and decolonised.
Closes #62