According to the following table:
* MOUSE_L -> DIG
* MOUSE_R -> PLACE
* SCROLL_UP -> HOTBAR_NEXT
* SCROLL_DOWN -> HOTBAR_PREV
This commit entirely removes the special KeyTypes used for joysticks.
Support for the MOUSE KeyTypes had already been removed in the main
game code without adapting the joystick code, breaking joystick
input. This commit restores joystick functionality.
* Various code style fixes
* Use range based for loops
* Use empty instead of empty objects
* Use C++11 default keyword for trivial constructors and destructors
* Drop some useless casts
* Use emplace_back instead of push_back to improve performance of some vectors push
* Add joystick type detection (with joystick_type setting to override it)
* Fix multiple joysticks from interfering with each other by only reading from one (add joystick_id setting)
* Add support for Xbox controllers
