CLI port: Allow to map NDS keys to joystick buttons.

[MasterEnoc]

• It allows to map NDS key to joystick buttons. Keys were mapped and then restored with load_default_config(), thus I remove it, however, looks like gtk frontends have a different keycode for joystick buttons, thus a user of both frontends will have to rewrite the config each time it uses one frontend or the other.

• it fixes config file processing, it now continues even when errors are found. Previously, mapping a NDS button to a joysticks buttons had to be sequencially, I. e. A, then B, then Select, etc. If any key was skipped in the corresponding order desmume would stop from mapping the keys.

• Add boost support for joysticks, currently it works in a hold fashion, I do not know if it should be changed to toggle, or both. Additionally, I implemented this in a very cheap way, I did not want to make big chances in the codebase, nonetheless, I could try to fix it in other way if you do not like it.