Export Kexi documentation from userbase to docbook

[Dimitrios T Tanis]

I'll have to agree on some points with Boemann.
I think it's just double the effort to put in. Offline documentation in 
Docbook trying to keep up with Userbase would be a hurdle and could 
confuse a new user.

As a solution an updated Docbook could be shipped along with each major 
release, ALWAYS having a link to the userbase. e.g. "Offline 
Documentation is for version 1.0. To view up-to-date documentation visit 
the online documentation pages available on userbase"