Sample and background weighting, source target flow sets separation, support for sampling and flow calculation pair generation policies

This major release introduces sample weighting and source/target sample.

• The sample to analyze can now be weighted, reflecting confidence in its involvement in a phenotype of interest
• It is possible to now supply a second set to analyze and bioflow will try to most likely connection between the two sets. This is useful in cases where two separate sets of interest have been identified, but the connection between them is unclear. For instance one is experimentally discovered hits, the other one are known effectors. Right now, the secondary set has to be disjoint from the primary set
• It is possible to now supply a weighted background set, and the nodes will be selected preferentially according to it. Thanks to that some nodes can be excluded from sampling or a more realistic background model introduced.
• BioFlow now supports the sampling policy, that can be assigned during the sampling process (including the auto-analyze) as well as flow calculation policy that generates the pairs of nodes that will be used to build the flow.