create DockableGuiSprite

Create DockableGuiSprite class that inherits off of Sprite. The purpose will be to create a gui class that will render graphics that stay static on the camera. This will be used for things like info bars, stats, on screen info, etc.

No files, tests, or entry points are named. Start by locating the Sprite class and the camera and rendering paths, then determine how a camera-static GUI object should integrate with them; done means a DockableGuiSprite exists and can render static on-screen graphics for bars, stats, or other HUD information.

Written by the indexing model from the issue text.