Tribes filtering

[gunchleoc]

This PR contains code to only load the tribes that are actually being used.

I am planning to use the same design for loading the world, so that defining units will become orthogonal again. However, this branch is already big as it is.

Note that I relaxed the testing requirements a bit, because conquering is not working properly in the editor. This could be tested by merging the scenario editor branch once it's usable again.

Coding changes:

• Map object types are registered in a new class DescriptionManager
• Each tribe only gets loaded when a player is playing as that tribe
• Buildings and immovables can still be placed via Lua,
  e.g. we can place a frisian_fortress if nobody is playing Frisians.
  If they need immovables with an attribute, these are loaded dynamically via the
  attribute.
• Support for custom scenario wares as well as workers and buildings
• Support for overwriting default units via scenario code
• Fix subdirectory handling in zip file system
• Player statistics and allowed ware/worker types are now stored in maps rather than vectors
• Make success of LuaFlag::set_wares independent of wares order
• Clean up some superfluous includes
• New test scenario that places all tribes' buildings
• Added new tests to market scenario and lua_testsuite for foreign and custom units
• Added a script for bulk renaming files with git mv. It just somehow ended up in this branch...

Changes to the Lua interface:

• For each init.lua, there is a register.lua.
  The register.lua registers the names and attributes with the engine, like this:

    return {
        berry_bush_blueberry_tiny = { "seed_berrybush" },
        berry_bush_blueberry_small = {},
        berry_bush_blueberry_medium = { "flowering" },
        berry_bush_blueberry_ripe = { "ripe_bush" },
    }

• Custom scenario units to be added to a tribe are now defined via a table rather
  than special Lua functions
• If you're overwriting a default unit without assigning it to a different tribe,
  just place an init.lua and register.lua below <scenario>/scripting/tribes.
  There's no need to list it in <scenario>/scripting/tribes/init.lua as well.

[Noordfrees]

Only two minor comments regarding the testsuite left, code LGTM. Will test this a bit more today.

[Noordfrees]

Then do please :)
This is the last nit, once this is done this is good to go in

[gunchleoc]

Thanks a lot for this big review :)