Move away from [+tag] macros about wesnoth

[CelticMinstrel]

With the advent of optional macro parameters, I wonder if perhaps it's a good idea to consolidate all the unit macros into a single macro for placing a unit… though I think this still isn't quite possible. I don't know of any way to have an optional parameter that makes the unit loyal if present, for example. We'd probably need something like #ifarg?