[Scip] multiple pricer

[Gerald Gamrath]

Hi Sebastian,

> The other option would be to have only one pricer that holds all the
> pricing problems and their data. Obviously, controlling the sequence of
> pricing problems would be easy in this case. Can you think of any
> reasons why I shouldn't do it this way?
no, that is exactly the way I have already done it in my projects and it 
worked well. I think that this is also the only way to run the pricing 
in parallel, if you do not want to change the SCIP core.

Best,
Gerald