Create a New Watchlist Tab in Account Tables

Let's create another tab in the Account tables called "Watchlist" for managing the following of certain assets. This would solve the long standing issue with certain default assets being forced to show up in Account as recently discussed in issue #579.

Almost all stock trading platforms include this feature. Now that we have a nice Portfolio here that tracks current market prices we could easily expand it to include a Watchlist feature in it's own tab as @wmbutler has suggested in issue #247.

Here is an example of a watchlist in action:
https://www.tradingview.com/chart/?symbol=POLONIEX%3ABTSUSD