Hide Transfer Data feature behind feature flag

bramble-api/src/main/java/org/briarproject/bramble/api/FeatureFlags.java

@@ -12,4 +12,6 @@ public interface FeatureFlags {
 	boolean shouldEnableDisappearingMessages();
 
 	boolean shouldEnableConnectViaBluetooth();
+
+	boolean shouldEnableTransferData();
 }

bramble-core/src/test/java/org/briarproject/bramble/test/TestFeatureFlagModule.java

@@ -29,6 +29,11 @@ public class TestFeatureFlagModule {
 			public boolean shouldEnableConnectViaBluetooth() {
 				return true;
 			}
+
+			@Override
+			public boolean shouldEnableTransferData() {
+				return true;
+			}
 		};
 	}
 }

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -307,6 +307,11 @@ public class AppModule {
 			public boolean shouldEnableConnectViaBluetooth() {
 				return IS_DEBUG_BUILD;
 			}
+
+			@Override
+			public boolean shouldEnableTransferData() {
+				return IS_DEBUG_BUILD;
+			}
 		};
 	}
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationActivity.java

@@ -376,7 +376,7 @@ public class ConversationActivity extends BriarActivity
 			menu.findItem(R.id.action_connect_via_bluetooth).setVisible(false);
 		}
 		// Transfer Data feature only supported on API 19+
-		if (SDK_INT >= 19) { // TODO also hide behind feature flag
+		if (SDK_INT >= 19 && featureFlags.shouldEnableTransferData()) {
 			menu.findItem(R.id.action_transfer_data).setVisible(true);
 		}
 		// enable alias and bluetooth action once available

briar-headless/src/main/java/org/briarproject/briar/headless/HeadlessModule.kt

@@ -96,5 +96,6 @@ internal class HeadlessModule(private val appDir: File) {
         override fun shouldEnableProfilePictures() = false
         override fun shouldEnableDisappearingMessages() = false
         override fun shouldEnableConnectViaBluetooth() = false
+        override fun shouldEnableTransferData() = false
     }
 }