Action chaining

After some months in development, we feel it is finally time to submit Action Chaining for merging in Spacewalk!

I prepared a screencast video to introduce the feature here (please excuse my English!):

http://turing.suse.de/~smoioli/Action%20Chaining%20screencast.webm

User documentation (Manager-branded, sorry about that!):

http://wiki.novell.com/index.php/SUSE_Manager/NewFeatures2.1#Action_Chaining

Some technical documentation:

http://wiki.novell.com/index.php/SUSE_Manager/ActionChaining

Code is divided in three parts:

1. reboot action changes by @mcalmer: these commits change the way rebooting works, and in particular when a reboot action is considered complete. Currently, a reboot action is complete as soon as the shutdown command is complete, which is not compatible with Action Chaining since other Actions could be executed before the reboot is actually carried out. With these patches, a reboot will not be considered complete until the whole power cycle is finished and uptime has decreased;
2. Database and Java Web UI code: this adds database tables and code to implement the Web UI plus utility classes also used by the XMLRPC API.
3. XMLRPC API: it's currently WIP, we plan to upstream it as soon as it's done (of course, if previous parts are accepted).

Further implementation notes in commit comments.

As usual, feedback is welcome!