simplify import_svg API

[snoyer]

Importing an SVG file from Inkscape using the labels set from the "Layers and Objects" panel currently requires passing both label_by="label" and is_inkscape_label=True to import_svg().

This PR proposes to remove the is_inkscape_label parameter and allow using label_by="inkscape:label" (matching the attribute as it appears in the XML: <path d="..." inkscape:label="foo" />)

The implementation is basically handling the inkscape: prefix in the label_by values as a shortcut for the actual {http://www.inkscape.org/namespaces/inkscape} namespace.
This should be future-proof enough to handle more shortcuts for other software in addition to Inkscape if the need arises (as opposed to adding more use_xxx_label: bool parameters as per the current approach)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.34%. Comparing base (25181f4) to head (393d64e).
Report is 72 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #838      +/-   ##
==========================================
- Coverage   96.98%   96.34%   -0.65%     
==========================================
  Files          31       31              
  Lines        8901     9129     +228     
==========================================
+ Hits         8633     8795     +162     
- Misses        268      334      +66     

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[jdegenstein]

Looks good to me

[gumyr]

Thank you!