Added marker icon customization option (#53)

[tpachmann]

Hi guys!

As promised in issue #53, I've been working on an easier way to customize the marker icons directly in the Grafana dashboard.
The changes introduce the functionality to adjust the global and point-specific marker styles without the need to rebuild the plugin (for a full explanation of the feature, please refer to my changes to the README.md):

Here's my (more or less) detailed list of changes:

• Added grouping for config options (General, Markers, Ant Path, Heat):
  

• Migrated to SVG icon (now defined inline with fully customizable color)

• Added config options for default (primary) & secondary marker icons:
  

• Usage of useMemo for createMarkers to improve performance

• Fixed invalid colors for Ant Paths (now using hex colors instead of the unsupported color names from Grafana)

Once again, feedback is highly appreciated :)

Best regards!
Tim

[xkilian]

@tpachmann How does this related to the WIP in #51 for multiple tracks which included :

• Custom SVG Markers for different timeseries by label value
• Custom AntPath colours for different timeseries by label value

From what I understand, what you are implementing is a little different than associating Custom SVG markers with label values. Using labels is really how I envisioned to differentiate dynamically types of devices (cars/buses/people/base stations/etc.)?

[tpachmann]

Hi @xkilian,

first of all thanks for your feedback!

The main idea behind these changes was a simple option to change the default marker icon and its color - I've added the point-specific overwrites to the styles just for the case that someone wants to style a few of the markers differently than the rest.
Tbh, I didn't really have the "multiple tracks" idea in my head and therefore actually missed out on the related work that has already been done in #51..

So this PR might indeed be kind of a duplicate to @eh-steve's approach in his draft (great work btw!) - the implementation for point-specific overwrites via labels is also a better idea than getting it directly from the data.

As #51 is still WIP and I don't really know the progress of it: Should I close this PR as a duplicate or adjust it to use the proposed label structure as an iterim solution?

[eh-steve]

I am planning to finish off my PR as soon as I get a chance but the code is pretty much done (just need README updates and adding example configs/screenshots). If you want to make any changes to that PR, feel free

[tpachmann]

Closing this PR due to existing related work in #51.