Improve path resolution for extensions.

[psilentp]

The inkscape extensions appear to need to extend the system path to include the extension directory. We should come up with a cleaner way of doing this than hard coding guesses into the scripts. It is also worth determining if this is still needed.

figurefirst/inkscape_extensions/1.x/tag_axis.py

Lines 3 to 5 in c8cad3d

	sys.path.append('/usr/share/inkscape/extensions') # or another path, as necessary
	sys.path.append('/Applications/Inkscape.app/Contents/Resources/extensions')
	sys.path.append('C:\Program Files\Inkscape\share\extensions')