editor: Remove tabbed viewer

Removed it pending rethink of interface.
general: Removed use of test data

Pending scene node implementation.
scene_nodes: Initial implementation
scene_nodes: Add UniqueId mix-in

* Provides unique identifiers for classes
scene_nodes: Add custom exception class

* Adds the NotFoundException
scene_nodes: Add scene configuration and nodes

* Creates an Attachable mix-in that can be used to attach entities
  to scene nodes. This is applied to mesh.
refactor: Make camera properties modifiable
state_machine: Make Qt state machine frame timer parameterized
General: Remove input directory from build

This was unused and is left out from the scope (for now)
Remove subclassing from renderer

Renderer is now composited into classes that provide an OpenGL context,
e.g. a Qt OpenGL widget.
Material: Add header for inclusion of all internal techniques
Loaders: Mesh loader returns smart pointer
Scene: Update test game states to use the new scene config

Also adds control to state data lifetime.
Rename test crate files
forward_rendering: Implement a blending forward renderer

* Render in multiple passes with early Z-pass
* Render one light per pass
* Unified code style for GLSL
  * CamelCase for uniforms and vertex attributes
  * underscore_case for varying and stack attributes
Qt: Fix Qt renderer buffer swapping
MeshLoader: Set unused members to 0
Add typedef for scene node IDs
Move scene config out from game state

Reduces coupling of state and what is visible.
Re-enable debug overlay