Added Two Symbolic Icons and Added Info to Icon Extract Script

Added two new symbolic icons to "desktop/icons/hicolor/scalable/actions/
	-mypaint-close-tab-symbolic.svg
	-mypaint-tab-options.svg
Added Useage txt to "svg/symbolic-icons-extract.py" script to lessen confusion
Lastly, symbolic-icons.svgz has the two new icons mentioned earlier under Actions

Fixes #17