Worked on improving the GUI.

- I added the graphics needed for scrolling and the in-game windows frame.
- I made the corresponding changes in cegui files to display the new scroll bars.
I'll work on the windows frame cegui changes in another commit.

Part of #5
Updated the credits files with latest info, and removed unused models.

Part of #93
Fixed GoldStack author to be Danimal.

Sorry again for the copy/paste error.
Added Chicken coop licensing info

Could you have a look @Danimal696 ?
Fixed the last file licensing info.

What's left is to change the font and split the OpenDungeons.png file into two files with separate license, and we're clean. :)
Split the GUI files and image to use proper licensing on each.

Part of #93
Replaced the blue highway font closed source font by the OFL MedialSharp one.

I also added the missing licenses.

Fixes #93
Fixed two CEGUI warning types.

(Std) WidgetLookManager::addWidgetLook -
Widget look and feel 'OD/ComboDropList' already exists. Replacing previous definition.

(Error) CEGUI::UnknownObjectException in function 'CEGUI::Image& CEGUI::ImageManager::get(const CEGUI::String&) const'
Image not defined:

I left those two:
(Error) Falagard::xmlHandler::elementStart - The unknown XML element 'DimOperator' was encountered while processing the look and feel file.

(Warn)	Property 'HorzExtent' is not writable so it's implicitly banned from XML. No need to ban it manually

Because those were correct in previous CEGUI versions and I'd rather make sure
how to fix those properly and they shouldn't break the game anyway.
Merge pull request #116 from Bertram25/development

Font + skin split