Name changed to "GDevelop"

As discussed [here](http://www.forum.compilgames.net/viewtopic.php?f=18&t=4947&p=45714#p45714), the software name is changing from "Game Develop" to **GDevelop** (easier to find with search engines, not used anywhere, it's shorter, sounds nice, is a shortcut for "Game Develop", and GD acronym can still be used).
@victorlevasseur if you have some time, could you check that everything seems ok with the change? I'll merge it soon, but if you have some time, do not hesitate to check out the branch, compile and see if everything seems ok. :smile: