Refactor plotting to enable transmission line path data

[danielolsen]

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• Is your feature request essential for your project?

Describe the workflow you want to enable

Currently, data in PowerSimData are only sufficient to map the start and endpoint of lines to coordinates. However, forthcoming grid models may contain a wider range of information, including true paths of transmission lines. For these grid models, it would be nice to be able to refactor the plotting functions to display this information, rather than just start points and end points.

Describe your proposed implementation

For functions that plot the network, we could have a flag that determines whether the lines are plotted as start- and end-points or as full paths. Path data would be associated with the branches themselves, as a list of 2-tuple (lat, lon) coordinates. Display colors and thicknesses could be the same for each segment of the line as they would be for a straight-shot line.

[merrielle]

Notes: related to HIFLD, may be good for @merrielle