Rework weapon scheme handling in frontend and fix a couple of bugs
There were many oddities in weapon scheme editing which are fixed now:
* When you left the weapon scheme editor, everything flashed briefly
* When you leaft the weapon scheme editr, the weapon scheme selection always reverted to Default. Very annoying
* Clicking on New or Copy now instantly creates and save the new weapons set
07f3bf8d98a3
Hedgewars.png had a resolution more than twice as high as required; also fixed some (mostly obsolete) code that also contained a typo that would cause a warning/note in clang