[packagekit] Add a per-Transaction ::Changed(void) signal and deprecate the other status signals

[Richard Hughes]

At the moment we have some nice properties on the Transaction
interface, and individual signals (ProgressChanged, StatusChanged,
AllowCancel and CallerActiveChanged). This obviously isn't good as we
need to write masses of code everytime we add a new property on the
interface. This is magnified three times, by doing the duplication in
each of the bindings.

Similar to other projects, they'll now be a single ::Changed() method
on the interface that is fired whenever one (or more) of the
properties change. The old signals will be deprectated, and removed in
0.6.x.

This should only affect binding people, as end-user applications will
be using the packagekit-glib or packagekit-qt bindings. 0.6.x isn't
going to happen for a few months, so the old signals are not going
away anytime soon. I know this seems like we're making changes for
changes sake, but I want to keep the project alive (and growing!) and
evolving to be more efficient and easy to use in end-user
applications. I appreciate the effort it takes to keep bindings up to
date.

Richard.

p.s. I've also added RemainingTime, ElapsedTime and Speed as new
properties on the interface too.