Multiple views or DataSource

[Jhsmit]

When adding a data source it might have multiple columns that need to be plotted in different graphs

currently, because x and y are specified in render_kwargs, this is not possible

it might be better to determine which column get plotted in render_sources

[Jhsmit]

The protein viewer also does work play together nicely with the current paradigm.

It needs to frequently shift between data sources, which is best done by having a data source coupled to it and then modifying that in-place
-> make a parallel system with DataSource object but one that is coupled to the Figure through the controller?

[Jhsmit]

fixed by #188