Define stable ordering for application favorites and running apps

Define stable ordering for application favorites and running apps

For both of these, because of optimizations a few patches ago, we
ended up relying on hash table ordering which caused instability
in the application well among other things. Define an ordering
for both.

The favorites is just the order of the GConf keys, and new items
get appended.  In the future we should allow insertion at any
point which the grid could use.

For running applications order, define a new "initially_seen_sequence"
transient variable which is just an monotonically incrementing
integer assigned to an application for the first time we saw it
running in this session.  When an application is closed, it's reset.