Add possibility to change keyboard / joystick mappings

[laamaa]

The configuration could be initially done through a config file, at some point possibly from the application.

[laamaa]

10 implements SDL Game Controllers for the program, meaning that most joypads should work now out of the box.

If bindings need to be changed, one can create a mapping string with external tools.

The keyboard thing must be still sorted out.

[peterswimm]

Can you point out what external tools we can use?

[laamaa]

https://generalarcade.com/gamepadtool/ haven't tested, but something like this should work

[laamaa]

Config file support implemented by JeffAlyanak