Removed private package declaration in device common bundle & added doc comments

components/device-mgt/org.wso2.carbon.device.mgt.common/pom.xml

@@ -30,7 +30,6 @@
                         <Bundle-Name>${project.artifactId}</Bundle-Name>
                         <Bundle-Version>${project.version}</Bundle-Version>
                         <Bundle-Description>Device Management Common Bundle</Bundle-Description>
-                        <Private-Package>org.wso2.carbon.device.mgt.common</Private-Package>
                         <Export-Package>
                             org.wso2.carbon.device.mgt.common.*
                         </Export-Package>

components/device-mgt/org.wso2.carbon.device.mgt.core/src/main/java/org/wso2/carbon/device/mgt/core/dao/DeviceDAO.java

@@ -41,7 +41,7 @@ public interface DeviceDAO {
 	/**
 	 * @param type       - Device type.
 	 * @param identifier - Device identifier.
-	 * @return
+	 * @return the Device object which matches given data
 	 * @throws DeviceManagementDAOException
 	 */
 	Device getDeviceByDeviceIdentifier(Integer type, String identifier) throws DeviceManagementDAOException;