Fix AppImage Crashes on Save Command

[danyeaw]

This PR sets the environmental variable XDG_DATA_DIRS so that Gtk can find the user-specific data files related to GNOME when compiled from source. Also, librsvg was failing to build and this updates the dependencies to fix that issue with the docker image.

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PR Type

What kind of change does this PR introduce?

• Bug fix
• Feature
• Chore (refactoring, formatting, local variables, other cleanup)
• Documentation content changes

What is the current behavior?

AppImage version of Gaphor crashes on save.

Issue Number: #1355

What is the new behavior?

No crashes

Does this PR introduce a breaking change?

• Yes
• No

Other information

[danyeaw]

I am getting the same error, so this isn't quite right.

[amolenaar]

Should we set the GSETTINGS_SCHEMA_DIR variable when the Gaphor is started maybe?

[danyeaw]

I think the issue is that XDG_DATA_DIRS was not set to where jhbuild's share folder was, and then PyInstaller didn't know where to find the GLib schemas.

[amolenaar]

Looks good.