Signal Android for LPC signal-server

This is a fork of Signal Android v6.20.6. The following relevant modifications have been made:

• app/build.gradle, app/src/main/res/raw/whisper.store, app/static-ips.gradle
  The server URLs have been set to dworkin.nl internal domains, and a dworkin.nl root certificate was added to the certificate store with Keystore Explorer.
• app/src/main/res/values/firebase_messaging.xml
  Updated to use the Firebase project msgserver-cloud for Firebase Cloud Messaging.
• app/build.gradle
  Server public params changed to a new value, generated by signal-server.
• libsignal/service/src/main/java/org/whispersystems/signalservice/api/services/CdsiClient.java, libsignal/service/src/main/java/org/whispersystems/signalservice/api/services/CdsiSocket.java
  Use a fake CDSI server built into signal-server.