application: asset_tracker: save power by triggering GPS update on motion

[plskeggs]

Add GPS_START_ON_MOTION to asset_tracker/Kconfig (default y for Thingy:91).
Add GPS_CONTROL_FIX_CHECK_OVERDUE to gps_controller/Kconfig; to be set longer
than *_INTERVAL value. Use GPS_START_ON_MOTION to conditionally change gps
reporting interval in gps_controller. Add motion_activity_state_t to motion.h.
Rewrite motion_handler() in main.c to detect activity/inactivity state.
Change structure of it to allow triggering of GPS at end. Add new function
motion_trigger_gps() to trigger GPS no faster than shorter
GPS_CONTROL_FIX_CHECK_INTERVAL on motion, otherwise revert to new *_OVERDUE
value to save power. Enhance gps_controller.c to keep track of most recent
time the GPS unit was powered. Use most recent time powered in
motion_trigger_gps() to ensure GPS not triggered immediately on every
movement (which hurts power consumption).

[NordicBuilder]

All checks are passing now.

checkpatch (informational only, not a failure)

No additional types will be considered - file 'scripts/checkpatch/typedefsfile': No such file or directory
-:490: WARNING:NEW_TYPEDEFS: do not add new typedefs
#490: FILE: applications/asset_tracker/src/motion/motion.h:36:
+typedef enum {

- total: 0 errors, 1 warnings, 443 lines checked

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[rlubos]

Looks good, just a few nits.

[plskeggs]

It's unclear to me why the Jenkins job has failed. There is no useful information I can glean from it to act on.