Merged the draft branch for 4.2 manual

[Wolthera]

Hey everyone,

I've merged the draft branch into master.

Stupidly enough, while I've tagged the branches, it seems the tags
don't get added to the repository. As I never before had to deal with
this, it may be that I am just not allowed to tag.

The translation scripty isn't pointed to the new gitlab situation yet,
so we can still make small changes in master.

Anyway, updated manual will be at docs.krita.org soon.

-- 
Wolthera