Optionally start minimized to tray

Restores mimized to tray if it was closed as such and adds an option to
force starting mimized to tray (if a tray is available). Fixed #1133
Fix duplication/dropping of messages in certain instances.

When multiple messages are processed at once, if one of the messages is flagged
for redirection, the wrong array is accessed, potentially causing the redirected
message to be dropped and another message to be duplicated.
Set minimum (the special value) timeout to 0

Fixes #1201
Add notification backend to support DockManagers

DockManager is a DBus API that does fancy icons. Current support
includes progress reporting whilst connecting, requesting attention
when highlighted and showing pending highlight count in a label. Exact
support also depends on the dock.
Don't crash if no audio file for Phonon is set