Inkscape is a vector graphics editor of Scalar Vector Graphics (SVG) documents, which is the tool we use for that purpose.
Can be "linked" or "embedded". This is configured in:
Edit→Preferences→Input/Output→Bitmaps→Import
You can also revert from one type to the other with:
Extensions→Images
The $\mathrm{\LaTeX}$ extension from Pauli Virtanen (Thanks Pauli). The official link seems to be here.
Default packages (such as laussy.sty) can be added in the file default_packages.tex:
laussy@azag:~$ locate default_packages.tex /usr/share/inkscape/extensions/textext/default_packages.tex
Inkscape stores its images as XML, so it can be hacked. From within Inkscape, Ctrl+Shift+X and then regexp the shit you find here. I provide an example to change opacity and line widths.