Don't store rendering mode in Texture

If this is a property of the texture itself, that fact should be stored
in the texture metadata. If it's a property of rendering, we should note
that when it's rendered, as we do after this commit.
Add AssetManager

AssetManager owns textures and is responsible for loading them, or
loading the new 'missing' texture if the file is unavailable.
Use AssetManager in Terrain
Implement Texture reloading
Use inotify to monitor for changed assets
legal: re-wrote copying.md, added 3rd-party licenses

added detailed guidelines to copying.md.
Merge branch 'master' of github.com:SFTtech/openage
doc: fixed markdown in copying.md
repo: added .mailmap

git shortlog now mirrors the names and email addresses in copying.md
Move finding python into separate CMake module.

See #40
Additionally CMake will find Python on OS X now. Fixes #16
Add OS X prerequesites section for OS X to building documentation
buildsystem: prettified the new findpython cmake module
Merge pull request #64 from svkurowski/add_osx_building_doc

Add OS X prerequesites section for OS X to building documentation
Draw version in lower left corner, take 2

 * Version drawing and FPS drawing now done in the same
   function, toggled by F3.
Add a screenshot manager, and let it save the screenshots with a nice name
Merge pull request #62 from franciscod/screenshot

screenshot: refactor with numbering and timestamping
Merge branch 'draw_version' of https://github.com/oldlaptop/openage into oldlaptop-draw_version

Conflicts:
	copying.md
	cpp/engine.h
doc/editor: initial ideas for the map/campaign editor
engine: removed 'version' text from version overlay
Merge branch 'asset_refresh' of ColdPie1/openage into inotify