Add Resoure to LDAP schema

- main.java will be generate also resources
- LdapConnector/Impl has new methods for work with resources
- EventProcessorImpl has new strategy to work with resources messages (from log)
ExecService class now extends PerunBean class.

- Add dependency on perun-beans to pom.xml in Controller, Engine, Rpc-lib, Rpc and Tasks-lib.
- Move ExecService from tasks-lib to perun-beans
- Modify toString method in ExecService
- Add serializeToString method to ExecService
GUI: display member mail in findCandidates()

- When adding new member from candidates, display member mail
  (if not present, display user:preferredMail).
Merge pull request #146 from zlamalp/candidate

GUI: display member mail in findCandidates()
Merge pull request #145 from stavamichal/Ldap-add-resource

Add Resoure to LDAP schema