We want to move away from using dconf inside the sandbox,
and instead use the keyfile backend for GSettings, which
has gained the capability to read defaults and locks.
This change makes the dconf database contents and locks
available in a suitable format. The files appear inside
the sandbox in the /etc/glib-2.0/settings directory.
We only export the default values for keys in the dconf
subtree whose path matches the app id, as well as prefixes
listed in paths key from the X-DConf group in metadata.
This commit adds a new dependency, since we're now linking
against libdconf.
Closes: #2295
Approved by: alexlarsson
f2303ee4c5