Branch: krita-colorchannels-silvioheinrich

[Silvio Heinrich]

Ok, this branch i made in preparation for the merge of the 
blending-modes branch.
It adds an icon next to the alpha lock icon in the layer docker.
It is there to enable/disable the alpha channel for layer compositing.
And it is now possible to lock/unlock and enable/disable each channel 
separately.
To do this i added a new set of flags (Channel Lock Flags) to 
KisPaintLayer and extended the Channel Docker.
I also fixed a little mistake with the naming of the channels.... Red 
and Blue where interchanged.
And there was some weirdness with indirect painting while a channel was 
locked (it only updated properly after the stroke was finished).
I fixed this too.

I will merge both the colorchannels and blendingmodes branches on Monday 
or Tuesday
if nobody wants to throw in a veto :D

PS: The icon i used for the Layer Docker is not this stunning... so if 
anyone can supply a better one, please do so :)