Merge pull request #124 from amccarthy/master

[connman-qt] Make TechnologyModel unavailable if there is no tech.
Bump version to 1.0.71
DEV: Add debug.
[connman-qt] Improve counter registration/unregistration behaviour.

During initial counter construction and property assignment the data
counter is registered and unregistered from Connman many times. Fixed
by keeping track of the registration status of the counter and only
registering or unregistering if necessary.