Add ShellVersion, designed for detecting OUT_OF_DATE extensions so they can't
be installed, as well as ApiVersion, designed for backwards-compatibility with
the SweetTooth web-app, which must support all shell versions.
https://bugzilla.gnome.org/show_bug.cgi?id=654770
GetExtensionInfo() takes a UUID and returns a JSON object with information
about that extension including their metadata, path and current state.
ListExtensions() takes no arguments and returns a JSON object mapping UUIDs
to the same information objects described above.
https://bugzilla.gnome.org/show_bug.cgi?id=654770
This is our convention.
The only exceptions are double quotes for words in comments that give
them a special meaning (though beware that these quotes are not truly
necessary most of the time) and double quotes that need to be a part
of the output string.
For various reasons I'd like a method which allows evaluation; say
log in from another machine and run "gnome-shell --repl" or something.
Also as a possible solution for the screensaver X grab issue, add
a (read/write) property "OverviewActive".
https://bugzilla.gnome.org/show_bug.cgi?id=596102
