Reorganise plotting module

[cpalfonso]

There are a few major changes in this pull request:

• New subduction teeth implementation with more consistent size/spacing parameters (now based entirely on display units, not data units)
  • This implementation should also be able to handle changes to the figure (e.g. updating axes limits) after plotting
• Refactor gplately.plot by splitting the module up into several files since the single huge file was becoming unwieldy
• Add a simple test for the new gplately.plot.SubductionTeeth class

[michaelchin]

See the code below. The seg0 and seg1 could be Point in some situation and it will break linemerge([seg0, seg1]). Could you please also look into this?

https://github.com/GPlates/gplately/blob/9a751e98ff1aff5869fe2eb6f400f490bb815c39/gplately/plot.py#L611-L624

[brmather]

@cpalfonso - a gentle reminder for you to look into the issue raised by @michaelchin

[michaelchin]

See the code below. The seg0 and seg1 could be Point in some situation and it will break linemerge([seg0, seg1]). Could you please also look into this?

https://github.com/GPlates/gplately/blob/9a751e98ff1aff5869fe2eb6f400f490bb815c39/gplately/plot.py#L611-L624

This happened to me in https://github.com/GPlates/gplately/blob/master/Notebooks/01-GettingStarted.ipynb in case you would like to reproduce the error.

[brmather]

@cpalfonso - can you revisit this again, please?

[michaelchin]

@cpalfonso if you would like to finish the subduction teeth improvement, it would be great if you could take care of #188 as well. Sabin reported this issue. You might need to contact him regarding how to reproduce the bug. Thanks.