Set default preferred positioning methods for Geoclue position source.

Set the default positioning methods used by the Geoclue positioning
source to all positioning methods.

Change-Id: I62196cc0203642838104cb5a0dafa06b1df29190
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Fix incorrect accuracy values reported by Geoclue plugin.

Initialize variables to valid (unknown) values as they will not be
assigned to if accuracy data is not available with the current position
update from Geoclue.

Change-Id: Icdca528da86df9a2a95acf1cc6704a9c39485fe2
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>