New option in options.cfg: canTransferCraftsInAirborne
Default: OFF

Have you ever dreamed that you can transfer a craft while it is airborne? I mean when there is a base - with a free hangar - it can reach with fuel, which is closer then the original base. And this way the craft does not have to reserve much fuel, so it can use the remaining fuel for intercepting.

Now you can do this. :)
Just turn on canTransferCraftsInAirborne in options.cfg, and you can transfer that craft to ANY base it can reach with its remaining fuel.
Of course if a craft can't reach the selected destination base, it won't show up in the transfer-items-screen.
And of course transfer can only be done if the destination base have a free hangar. (not momentarily-free, completely-free!)
These type of transfers does not cost money, since the craft goes using its own fuel. :)
Crafts currently on the base are not affected, the normal rules applies to them.
Buttons' pressed state on the Graph screen is now saved to options.cfg
Changed: Graph-buttons pressed state is now saved in the Savegame instead of options.cfg.
option to turn off getError() for OpenGL, warnings

clang complains when you don't handle all the possible values of an enumin a
switch

Conflicts:
	src/Engine/OpenGL.h
Merge pull request #356 from hmaon/opengl

option to turn off getError() for OpenGL, warnings
Merge pull request #353 from fenyo1/saveGraphButtons

Buttons' pressed state on the Graph screen is now saved to the savegame
Merge pull request #343 from fenyo1/canTransferCraftsInAirborne

New option in options.cfg: canTransferCraftsInAirborne