add edge filtering options at build to help with memory constraints

[risserlin]

To help make large networks more manageable give the user options on how to filter the edges before the network is created. For instance:
For big papers (with more than X autors):

1. all authors are connected to the last author (instead of all pairwise connections)
2. all authors are connected to central node that is the paper
   Filter out:
3. uncited papers
4. any nodes that are not internal (for the case when you want to see who is collaborating in the same institution)
5. remove connection based on a single paper