cancel comms when signal is weak (RSSI < 5%)

to show which variables change throughout the course of the method

Previously the PumpStatus' event date was used to calculate the next poll.
Up untill change 045bebb3, this date was
set from the SGV date we got from the pump, see
https://github.com/jotomo/600SeriesAndroidUploader/commit/045bebb3a2021b523631deec76e8b8d47f7112dc#diff-20721b0d1f2575ca0cce44c52a932d36L193
After that change, the event date property is the time the record was created.
Hence, now the sgvDate property must be used to acquire the timestamp
of the SGV to calculate the next poll time properly.

Add missing imports.
Prep for release 0.5.0 - Sandgroper

Add “Check for App Update” menu item.
Don’t render trend arrows using HTML - use Unicode instead.
Rename app from “NS 600 Series Uploader” to “600 Series Uploader”.
Experiment with adding status tiles.

Beginnings of Update check feature

Upgrade to Gradle 3.3, Build Tools 25.0.2, Realm 3.1.2
Remove duplicate MedtronicCnlAlarmReceiver
Fix crash when viewing Registered Devices after package updates.

remove useless logging

Fix graphing
Fix for Realm hard crash

A few small changes that catch rare errors with the CNL specially when signal is weak.