Make hitting players make a visual damage flash to the player texture and the screen of the local player

Remove stuff made obsolete by making players more ActiveObject-like and raise protocol version number by one (because it is not compatible at all anymore)

Remove +"^[forcesingle" from ContentFeatures::setInventoryTexture, because 1) it was not used, 2) if it will be used, it won't need to do that anymore

Fix getTextureRaw to always return an image that is not in the texture atlas and fix plain "^[forcesingle" handling