akonadi shouldn't be launched on startup

On a default kubuntu setup the clock widget is the only thing that uses akonadi on startup.
If we change the default value of displayEvents to false akonadi wouldn't be started unless the user launches kmail or another application that needs akonadi.

Additionally we should disable the "Calendar Events" kwrunner which is in plasma-runners-addons (not installed by default).

See also http://majewsky.wordpress.com/2011/10/10/reducing-the-memory-footprint-of-akonadi/

TEST CASE:
- start a kubuntu session
- notice that akonadi is running ("akonadictl status" says Akonadi Server: running)
- install updates from oneiric-proposed
- restart the session (logout, login) and make sure you don't autostart any kde pim application (e.g. kmail)
- notice that akonadi is _not_ running ("akonadictl status" says Akonadi Server: stopped)