android: make JitsiMeetActivity.join public

android/sdk/src/main/java/org/jitsi/meet/sdk/JitsiMeetActivity.java

         return fragment.getJitsiView();
     }
 
-    protected void join(@Nullable String url) {
+    public void join(@Nullable String url) {
         JitsiMeetConferenceOptions options
             = new JitsiMeetConferenceOptions.Builder()
                 .setRoom(url)
         join(options);
     }
 
-    protected void join(JitsiMeetConferenceOptions options) {
+    public void join(JitsiMeetConferenceOptions options) {
         getJitsiView().join(options);
     }