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Temporarily increase zoom level

Color overlays.
overlays: Color/Animation overlay test images

Includes a color overlay template for as_woodentower0 and an
animation overlay template for as_lumberjack_barrack0.

All of this (including directory layout and naming conventions) is
temporary and likely to be changed later.
overlays: Color overlays for building instances

Requires fife branch `overlays`.
helios deserves all the thanks for making this possible.

Looking for `color_idle` as overlay for the action `idle`.
overlays: Start work on inventory overlay component
Ugly attempt to fix the initialization problem
overlays: More work on inventory overlay component

A better structure for the component, with more well-defined methods and
some properties as more readable shortcuts for FIFE-based stuff that is
needed every now and then.

Also adds more clear documentation, some TODOs and error handling.

As for `remove()`:
I left some questions about how the base image is supposed to be handled
in the respective code. This should ideally be clarified with FIFE to not
cook up some custom haphazard "solution" - maybe we can even get a nice
interface built into FIFE.