#91 Add options that control whether dbus and Tracker are started

[Ralph Böhme]

Add two new options that control whether we launch dbus and start Tracker with tracker-control:

start dbus    = yes|no (default: yes)
start tracker = yes|no (default: yes)

If Spotlight support isn't enabled or compiled in, the services aren't run in any case.

[Ralph Böhme]

Delivered in [c438f9a125450a4c5da252f8172411f0b55ceef3] for 3.1.2.