package: add support for split launcher/service apps

In the future, all apps will be dbus activated, and only install
a shim launcher in $(bindir). Add support for that with launch()
method that takes the package name (which must also be the application id
in the new app model)
Move application to the new deployment format

Make the application DBus activatable, and make sure that all
files in shared directories (except for the launcher in $bindir)
are in reverse dns notation.
city: overlay the side bar rather than pushing the content

Pushing the content when opening the side bar has the odd effect
that the window expands in the opposite direction (as the content
cannot shrink anymore).

https://bugzilla.gnome.org/show_bug.cgi?id=695222
Activate the application when running from source tree

This way it's again possible to debug the app without installing,
"simply" by running ./src/org.gnome.Weather.Application
(tab completion helps here)