This causes meson to automatically build the clapper gsettings schemas
and set GSETTINGS_SCHEMA_DIR to the correct location within the devenv.
This means that can now be ran without needing to install it somewhere
using:
meson devenv -C <builddir>
clapper
exit
More devenv overrides should be investigated (such as automatically
adopting the correct directory for translated locales etc.)
Signed-off-by: Florian "sp1rit" <sp1rit@disroot.org>
