Add mechanism to login to CareLink and retrieve HMAC and key for the attached device.

.idea/inspectionProfiles/Project_Default.xml

.idea/libraries/appcompat_v7_21_0_3.xml

.idea/libraries/commons_lang3_3_4.xml

.idea/libraries/support_annotations_21_0_3.xml

.idea/libraries/support_v4_21_0_3.xml

.idea/misc.xml

.idea/workspace.xml

app/app.iml

app/build.gradle

app/src/main/AndroidManifest.xml

.../java/com/nightscout/android/dexcom/DexcomG4Activity.java

...ain/java/com/nightscout/android/dexcom/LoginActivity.java

.../com/nightscout/android/medtronic/MedtronicCNLReader.java

...com/nightscout/android/medtronic/MedtronicCNLSession.java

.../nightscout/android/medtronic/data/CNLConfigContract.java

.../nightscout/android/medtronic/data/CNLConfigDbHelper.java

...om/nightscout/android/medtronic/message/MessageUtils.java

...ut/android/medtronic/message/ReadInfoResponseMessage.java

...tscout/android/medtronic/service/MedtronicCNLService.java

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