Refactors image loading and ownership to it's own class and out of SpriteRenderSystem.
Adds status icons reflecting the current damage state of the selected jet and target jet to the user interface.
Merge pull request #65 from absolom/stat_icon

Closes #54.
Implements a straight maneuver that can be queued.
Merge pull request #66 from absolom/straight_path

Closes #58.
Merge pull request #63 from absolom/network

Pull Request - Networking
Adds toShort and valueOf to ZOrder enum. Changes network transfer of zorder to xmit a short instead of a string representation.
Merge branch 'master' into network
Adds support for icons to network client and server.
Switches sprite image referencing to use an enum instead of a string.