Demo Network

[chrtannus]

• Provide a demo network which users can quickly load.
• Don't query the iRegulon services for that, but use the same static data every time.
  Use this gene list from the iRegulon tutorial, along with default query parameters and the iRegulon results.
• Also the demo data probably doesn't need to be saved in MongoDB, unless it's more convenient to do so. Either way, don't save/update node positions or the network topology (e.g. when the user checks another TF in the data tables) -- see Database Persistence #7.
  That means the network will be recreated in its original state every time.
• Do not save the demo network in the browser's "Recent Networks" list either.