Make it possible for panels to go all the way to the edge of the
shell. This is particularly important for panels that scroll, such
as the new power panel. All other panels are changed to compensate
for the loss of external padding.
https://bugzilla.gnome.org/show_bug.cgi?id=691229
This makes loading faster, with less I/O, avoids unnecessary
code duplication (around 1k lines shaved), and ensures that
all the panels link and work appropriately.
By the same token, it will stop external panels from being
created, and loaded.
https://bugzilla.gnome.org/show_bug.cgi?id=690036
Instead of either hard-depending on Tracker being installed, or crashing
when the Tracker GSettings schema is not found, make the configuration
insensitive if the schema is not available.
https://bugzilla.gnome.org/show_bug.cgi?id=687490
