Allow changing version warning banner text

[FranzRoters]

Currently the text shown by the version warning banner is fixed, e.g. for the development version it says: This is documentation for **an unstable development version**.

This is a pretty hard statement. Actually we do not consider our develpment code being unstable. When published it has been running through the same tests as the release versions. We would, therefore, apprecheate being able to edit the default text, e.g. via some theme variable.

[Carreau]

Would it be ok to edit only the an unstable development version text, that is to say only what is in bold ?

As this is done via javascript it might be annoying to allow configuration of text while still allowing formatting bold ... etc.

Or we just allow full html which I'm not a big fan of.

[FranzRoters]

Yes, from my perspective that would be absolutely fine. You certainly know the details much better than me, I didn't even think about formating, let alone the technical details. I agree that full html would be rather error prone.