Add settings.ini setting and hwengine param to disable holiday silliness (hat changes, etc.) settings.ini: In section [misc], add "holidaySilliness=false" hwengine: Add --no-holiday-silliness to command-line

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.