Render transformer graph labels in Screen coordinates

[dmronga]

This improves readability of the transformer frame names by rendering them in screen coordinates and setting a reasonable character size

[doudou]

Damn ....

I was telling myself "super awesome, I want to try it right now, improving text readability !!!!"

But then:

This new scheme is even worse than before for frames generated for SDF for the transformer, which makes the rock-transformer display even more unusable. At least, before, I could set a nonzero value to the joint and read the text, which doesn't work anymore.

I'm afraid this will have to at least be controlled by a configuration flag ...