Log 2D -> 2D transformations in the transform hierarchy

[nikolausWest]

Add ability to log image transforms like rescale or perspective distort between 2D spaces.

[nikolausWest]

Depends on

• Unify 2D and 3D renderer #350

[Wumpf]

Related to

• Automatically project 3D -> 3D from child to parent space #375

[Wumpf]

• [low prio] 2d equivalent of furstum to indicate 2d-2d transforms?

[nikolausWest]

Related: #1510