add unsubscribeGroup; add missing subscribe methods; refactor javadoc comments for subscribe methods
add unsubscribeGroup; add missing subscribe methods; refactor javadoc comments for subscribe methods

mohamed20102241/java,MattB101/java,MattB101/java,VanThanh12195/java,VanThanh12195/java,biddyweb/java,pranjalpatil/java,pranjalpatil/java,pranjalpatil/java,biddyweb/java,NizarBoussarsar/java,vyshakhbabji/java,sweetticket/java,biddyweb/java,ballbo/java,sweetticket/java,NizarBoussarsar/java,vyshakhbabji/java,NizarBoussarsar/java,mohamed20102241/java,ballbo/java,ballbo/java,sweetticket/java,VanThanh12195/java,MattB101/java,vyshakhbabji/java,mohamed20102241/java