Issue #1 - Deactivate GPS updates on survey tab change

* When a geolocation question is registered to receive updates and
another tab is pressed, the GPS updates are no longer needed.
* 'Next' button and Tab explicit click flows are now merged.
* Keep track of current Tab index.
* Leave accuracy status as is, since the location is also kept. Only
'Searching' indicator is restored when the GPS updates are removed.