Fixed a problem with equal endpoints of wps servers
The WPSMonitor has allowed multiple entries of wps servers with the same endpoint (uri). This is a problem for the WpsMonitor-Client which is currently in development. The solution for this problem is not "clean" yet, because the data layer should  manage such constraints. With this fix, the control layer handle this. The problem is, that JPA maps the java URI-Datatype as a binary large object which the database can't compare. Maybe the WpsEntity should be adapted (use String instead of URI for the uri datafield).