Add price charts to Converter and Auction screens

[pablen]

Closes #414

[gabmontes]

@pablen the charts look very nice! Some comments to discuss:

• When the window is reduced to its minimum size, the auction chart falls of the screen and the converter chart pushes the "Convert" button off the screen too. We should consider a different placement or min window size?

• The default chart timeframe should be 1 day to show more useful data to the users.

• The data is retrieved every time the tab changes and that should be cached (not necessarily persisted).

• Is the data updated in realtime? It looks like it is not.

• The build is failing. Should investigate the reason before approving/merging.

[pablen]

Closing for now as we'll move this new feature into the next major release.