Clean up lint warnings

.../java/info/nightscout/android/medtronic/MainActivity.java

...info/nightscout/android/medtronic/MedtronicCnlReader.java

...roid/medtronic/message/CloseConnectionRequestMessage.java

...t/android/medtronic/message/PumpStatusRequestMessage.java

...out/android/medtronic/message/PumpTimeRequestMessage.java

.../android/medtronic/service/MedtronicCnlIntentService.java

...nightscout/android/model/medtronicNg/PumpStatusEvent.java

...ightscout/android/upload/nightscout/NightScoutUpload.java

app/src/main/res/layout/activity_status.xml

app/src/main/res/values/strings.xml