Transform manipulators

[karnkaul]

3D transformation manipulators are quite useful, especially for translation and rotation (scale is more useful for authoring levels using prefabs etc).

Let's start with adding support for translation:

AC:

• Must be toggle-able
• Use a single mesh for all three arrows, or use instancing; three draw calls is not acceptable

Note: Interaction can be handled in another Issue, it will require ray-cylinder / ray-cuboid collision and mouse position => world space unprojection