RPC: fix updateNameTitles method

Method updateNameTitles called wrong method from core (updateUser) so it
can change not only titles of a user. Also updateUser in core can be
executed only by perun admin.

Now updateNameTitles from RPC calls updateNameTitles from core.
Fix logging in method deleteResource (core blImpl)

- there si calling of method removeGroupFromResource from Impl, need to add log message here
- there is log message about deleting resource which do not need to use affected groups
Merge pull request #144 from stavamichal/core-delete-resource-log-fix

Fix logging in method deleteResource (core blImpl)
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()