Add SetRead request (implemented as part of ModifyConfererenceRequest)

Author: rubengees

library/src/main/java/com/proxerme/library/connection/messenger/request/ModifyConferenceRequest.java

@@ -33,6 +33,11 @@ public class ModifyConferenceRequest extends MessengerRequest<Void> {
      */
     public static final String UNREAD = "setunread";
 
+    /**
+     * Sets a conference as read.
+     */
+    public static final String READ = "setread";
+
     /**
      * Blocks a conference.
      */
@@ -92,7 +97,7 @@ protected String getApiEndpoint() {
         );
     }
 
-    @StringDef({UNREAD, BLOCK, UNBLOCK, FAVOUR, UNFAVOUR})
+    @StringDef({UNREAD, READ, BLOCK, UNBLOCK, FAVOUR, UNFAVOUR})
     @Retention(value = RetentionPolicy.SOURCE)
     @Target({ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER})
     public @interface Modification {