- add license headers to everything
- convert a few files from public domain or LGPL2.1+ to GPL2+
- some archaeology to clarify which files are from which library

Found using `codespell -q 3 -w --skip="*.svg,*.po,*.ts,./share/tutorials,./src/libavoid,./packaging/win32/languages,./man,./src/2geom" -I ../inkscape-whitelist.txt`
whereby whitelist file contained:
```
dum
iff
glight
substract
te
upto
```

(bzr r10559)

(bzr r8254.1.28)

Fixed other xml files to have xml file declaration before comments.

(bzr r8254.1.27)