calls: add conference support

Change-Id: Ib72f0fa032a19aca867e155ade3df114854bae19
diff --git a/ring-android/app/build.gradle b/ring-android/app/build.gradle
index 4a259cf..f1015d6 100644
--- a/ring-android/app/build.gradle
+++ b/ring-android/app/build.gradle
@@ -78,7 +78,7 @@
 
     implementation "androidx.core:core:1.2.0-beta01"
     implementation "androidx.appcompat:appcompat:$android_support_core_version"
-    implementation 'androidx.constraintlayout:constraintlayout:2.0.0-beta2'
+    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
     implementation "androidx.legacy:legacy-support-core-utils:$android_support_version"
     implementation "androidx.cardview:cardview:$android_support_version"
     implementation "androidx.preference:preference:$android_support_core_version"
@@ -87,6 +87,7 @@
     implementation "androidx.leanback:leanback-preference:1.1.0-alpha02"
     implementation "androidx.media:media:$android_support_core_version"
     implementation "com.google.android.material:material:$material_version"
+    implementation 'com.google.android:flexbox:1.1.1'
 
     // ORM
     implementation 'com.j256.ormlite:ormlite-android:5.1'