Add reseting last NTP update time-stamp

:Release Notes:
Allow system-time update from NTP be more frequent than now.

:Detailed Notes:
Add last NTP update time-stamp reset on:
- setting date-time
- changing useNetworkTime to state off

:Testing Performed:
Desktop build.

:QA Notes:

:Issues Addressed:
[GF-52309] [GFP2TestPass] Settings - Incorrect time is displayed on Home screen after changing time manually and returning back to auto.

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: I76b1705bbacf486bcb7fd88f729431c735076b8b
Reviewed-on: https://g2g.palm.com/4007
Reviewed-by: DCO Verification
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>