preview-mode: Add grob-names option
preview-mode: rotate grob names to 45 degrees

I tried this because it seems to increase the chance the names are readable.
With the previous 90 degrees _all_ the names in my test scores
where printed on top of each other.
preview-mode: Remove text option from grob-anchors

Harm's original snippet combined anchor points with grob names.
This was unnecessarily complex.
Now there are separate files/functions for the two options