use the locally installed keys.*.html instead of connecting to the web

Originally reported in Debian: https://bugs.debian.org/850771.

The Inkscape "Help" menu needs internet access to work. This is annoying for airgapped users.

IIRC most of the menu items link to non-DFSG content, but one menu item is easy to fix: inkscape_help_keys.inx. The inkscape source package contains the same content.

Please install these somewhere like file:///usr/share/doc/inkscape/html/ or file:///usr/share/inkscape/doc/html/, and patch inkscape_help_keys.inx to point to them instead of http://inkscape.org/doc/keys092.html.

There is one problem with language detection. I presume the HTTP version does this via Accept-Language. The keys.*.html files don't link to one another, so inkscape_help_keys.inx or launch_webbrowser.py might need to be extended provide equivalent functionality based on $LANG?

Inkscape Version and Operating System:

Inkscape Version: all versions till now :)
Operating System: all Linux.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information