smarter associations

- handles polymorphic associations
- handles `x through: y` associations
- adds specs for association_processor

Change-Id: I09c9a91543dd2e699835a07cdb16b75cfd789320
fix readme example

Change-Id: I23cd8522e79252d4e1115106fa17bb0e87a6aa3d
Merge "fix readme example"
adds ability to hide isolated nodes on network graph

also:
- network.json nodes are now uniqued by name
- network SVG styling tweaked for better readability

Change-Id: Ie7650dd37ed337b18fce344583d174dab6204fb1
Reviewed-on: https://gerrit.instructure.com/44502
Reviewed-by: Jon Jensen <jon@instructure.com>
Product-Review: Jon Jensen <jon@instructure.com>
QA-Review: Jon Jensen <jon@instructure.com>
Tested-by: Michael Ziwisky <mziwisky@instructure.com>
Merge branch 'master' of gerrit:society