Use the proper prefix for our resources

Our ID is org.gnome.Weather.Application, so the path should be
/org/gnome/Weather/Application
package: add support for loading JS from a GResource

Load two resources by default, ${name}.data and ${name}.src, from
a gresource file in datadir. If the latter exists, set up gjs to
import modules from there.
Convert to load sources from a GResource

Compile sources into a GResource file and load that instead
of individual JS files.
For ease of development, when running uninstalled we still
load the JS files (and thus don't require a make first)
Update libgd