Put global constants like pixels per tile into a single place.
Move computing visible tiles into World.
Minor formatting fixup.

For whatever reason the lack of this space totally confuses QtCreator
into indenting everything by some 40 columns...
Extract rectangle clipping into its own function.
Compute influence zones for strongholds and villages.
.gitignore: add QtCreator autosave files.
Make TextureBank take care of its own instances.
render: draw borders of influence zones.