New creature window graphics

For discussion/feedback. Will be merged once finished.

Almost finished creature window, using graphics from this post on forum:
http://forum.vcmi.eu/viewtopic.php?p=11048#11048

As of now this is mostly finished, the only missing piece is upgrading commanders' abilities, will be implemented soon.

This branch also includes some graphical assets. I'm going to include them into repository in order to make VCMI functional without any additional packs. "Sources" for them (e.g. xcf files) will be uploaded into a separate repository called vcmi-assets along with list of authors. All assets will be licensed under CC-BY-SA - same license we already use in some of mods.

Note: initial discussion is in this commit: 7a9547b