Create PrivateGroupManager Facade and stub implementation

briar-api/src/org/briarproject/api/privategroup/PrivateGroupConstants.java

@@ -0,0 +1,22 @@
+package org.briarproject.api.privategroup;
+
+import static org.briarproject.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+
+public interface PrivateGroupConstants {
+
+	/**
+	 * The maximum length of a group's name in UTF-8 bytes.
+	 */
+	int MAX_GROUP_NAME_LENGTH = 100;
+
+	/**
+	 * The length of a group's random salt in bytes.
+	 */
+	int GROUP_SALT_LENGTH = 32;
+
+	/**
+	 * The maximum length of a group post's body in bytes.
+	 */
+	int MAX_GROUP_POST_BODY_LENGTH = MAX_MESSAGE_BODY_LENGTH - 1024;
+
+}