Profit history plot is worthless

[ryanholmdahl]

It's plotting every coin on the same set of axes, which after a few hours becomes absolutely unreadable.

I think there are two things we should do:

• [ ] Replace with a plot that just tracks the device's profitability over time, not every coin on that device
• [ ] Redo the coin history plot with a better plotting library to build interactive plots that aren't unreadable blobs