[WIP] Add trace2d plot

[jeiros]

Proposed Feature / Bug-Fix

First proposal for the API of a 2D trace plot, as suggested in #105

One thing I have not been able to figure out is how to add 'lines' that connect the dots. For that, one would have to use pp.plot but that does not accept colour mapping to a series of values, which we need.

Example Figure

PR Check-list

• Example added
• Tests added
• Docs added
• Changelog updated

[msultan]

This is such a cool plot to have have! +1 to @jeiros for getting this into MSMExplorer.

[jeiros]

Thanks @msultan ! If you have any suggestions or improvements on the design of the function let me know!

Something that I've thought about adding is an argument to allow the user to pass a list of labels in case he's passing a list of arrays and wants to know which colour is mapping to what trajectory.

Because at the moment it just looks like this:

So can't know which trajectory is doing what.

[msultan]

yea, the only way to do something more is to start implementing bokeh or plotly style interactive line plots that tell you the trajectory names as you hover over them. Otherwise, I think the best scenario right now is to write some helper functions that can find interesting trajectories though that is hard to define.