Some bugfixes

Commit a658822 adds key_mission to the controls group. Without this, the same key can be bound to "Show mission" and one of the other "More controls..." at the same time.

Commit 5a35c43 fixes mouse (and joystick) weapon cycling for heretic and hexen. Buttons could already be configured for this in setup, but they didn't have any effect. On a sidenote: this commit also fixes a (possible) boundary error, since the heretic and hexen "mousearray" was hardcoded to 4 items instead of to "MAX_MOUSE_BUTTONS + 1".