Text has point_size and pos properties

And text always draws in that point size, even if inside a viewbox. There are two things to fix, see todo items:

* Is the pointsize correct like this?
* How to prevent recompilation on each draw?
We do something similar in Widget, there we actually *assume* the user has not set a different kind of transform. Do you suggest to leave transform alone, and set position via GLSL?