update manager to become more modular

In my last post I wrote about how I got accepted for GSoC09 and am going to work on update manager. Now I couldn't wait for the actual GSoC09 coding period to start and created my own update manager branch right away and started hacking.

So far I have only written a few lines of code, but my mentor Michael Vogt and me came to the conclusion that whilst working on the internals of update manager it might be a good idea to make the whole program more modular.
Right now all the different functions of update manager (being the UI/frontend and the package manager interface/backend) are mixed up in various files, which makes not only reading the code harder, but also extending update manager more difficult. This was reason enough for me to have a look into making update manager more modular in its design and some of my efforts can already be seen in my update manager branch.

If you have any comments on the proposed backend interface or see major problems with it, please let me know, I would really appreciate some input on that. Also, the UI and the distribution-specific code interfaces are next on my list, before beginning to actually move existing code around. I hope to be able to finish that work before the GSoC hacking period starts, so I can concentrate entirely on my task of making update-manager distribution independent.