jira-integration: Add missing protected constructor to JiraConfiguration

Missing protected constructor in order to avoid wrong usage of the class (maybe
someone could try to do "new JiraConfiguration()" instead of
JiraConfiguration.create()).

FEA: ItEr77S16JiraAndTimConnectorContributionIntegration

libreplan-business/src/main/java/org/libreplan/business/common/entities/JiraConfiguration.java

@@ -37,6 +37,11 @@ public class JiraConfiguration extends BaseEntity {
 
     private String jiraPassword;
 
+    /**
+     * Constructor for Hibernate. Do not use!
+     */
+    protected JiraConfiguration() {
+    }
 
     public boolean isJiraActivated() {
         return jiraActivated;