Added an armature system for 2D animatable characters.

- modified the build.sbt to include the "config" library from TypeSafe.
- Added a drawArray() method in VertexArray that allows to ignore the
indices array.
- Added a shader for armatures.
- Added the Armature system which is both a DSL to describe the
armatures easily (like a file format) and a way to represent them in
memory and display them.