Weapon Panel - The Best of Both Worlds

Unfortunately, my changes from !85 (merged) have not been fully satisfactory for squarish panel shapes, sorry about that.
However, the reversion with !102 (merged) also brought back the mentioned issues, which are especially problematic if the panel is supposed to be attached to the screen edge.

Therefore, I present to you the new cvar hud_panel_weapons_onlyowned_maximized
The user can now choose between the two implementations.