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

Lua scripts for engine testing. These scripts are the same as other Lua scripts
in Hedgewars, but you ought to call `EndLuaTest(TEST_SUCCESSFUL)` or
`EndLuaTest(TEST_FAILED)` when the test is completed.