Due to the fact that the points renderer does not know for sure
which attributes will be used for rendering, it is now mandatory
to provide both vertex/fragment shaders for rendering AND hit
detection.
The hit detection shaders should expect having an `a_hitColor`
that they should return to allow matching the feature uid.
This will be all one eventually by shader builders under the hood.
Now most attributes will be custom ones defined by the user of the renderer.
The hit detection is broken for now and still has to be fixed.
Also it is not possible anymore to give a texture to the renderer,
this will have to be fixed as well.
Now testing with two features and adding a call to `prepareFrame`
without which the final render transform was off.
Also added a test with a pixelratio > 1.
