Devices were not properly reset at each frame, which caused
button_pressed() and other functions to fail.

This lets us get rid of m_autorelease and m_destroy and we’ll be able
to implement init_game/init_draw later, for stuff that must happen
on the render thread.

Controller::WasKeyReleasedThisFrame() is now keyboard->key_released() so
there is usually no need for a controller. They will completely disappear
when joystick axis binding has been ported to InputDevice.

Most input and GUI files are now in a common ui/ directory. The platform/
directory is no longer, as everythyng was moved to application/ or ui/.