Fix icon name for XDG mimetypes

The default icon for XDG mimetypes is the name of the mime with '/'
replaced with '-', unless the mimetype has an 'icon' attribute (and
solvespace-mime.xml does not have it). So the right icon name for
application/x-solvespace is 'application-x-solvespace', not
'application.x-solvespace'. Hence, properly rename the mimetype icons
in non-flatpak and non-snap installations.

Version 3.0

Improved de_DE

See solvespace#890 and its changed menu item

Version 3.0, release candidate 1

Version 2.3

Release 2.3 is a bug-fix release.

Version 2.2

Release 2.2 is a bug-fix release.

Version 2.1

Release 2.1 introduces *nix compatibility, internationalization,
technical drawing mode, rewritten DXF export, DXF import, and many other
minor features and bug fixes.

Version 2.1, release candidate 1

Release 2.1 introduces *nix compatibility, internationalization,
technical drawing mode, rewritten DXF export, and many other minor
features and bug fixes.

Version 2.0

This version is the first public release of SolveSpace, relicensed to GPL.
The commit marked with this tag contains the same source code as
the "solvespace-rel2.0.zip" archive distributed from http://solvespace.com.