qtcomponents documentation

[Marco Martin]

Hi all,

I think we should do a real documentation sprint for the plasma qtcomponents, 
to have a good api doc for the 4.8 release.

I have now merged the branch plasma-components-doc as the documentation was 
already good (and avoiding conflicts with master)

I have to say congratulations to who woked on it, let's complete and make it 
rock for 4.8 ;)

Cheers,
Marco Martin