GUI: implemented many usability fixes

- Reimplemented headers of inner tabs (longer ends with ellipsis).
- Shorten most of inner tab headers (context is present in gui header anyway).
- Added non-clickable screen-shield below all inner tabs, so user can't
  accidentally click on underlaying tab content.
- Added input validation to QuotaChangeRequest tab.
- Updated design of ExecService's details page
- Allow to edit ExecService details (enable/disable).
- Updated some adding tabs to allow incremental adding with
  notice, what was already added (member to groups, group to resources).

- Added filtering on service required attributes.
- Updated ExecService to be PerunBean.
- Added callback to update ExecService.
RPC: updateExecService must return updated object

- updateExecService() method in RPC now returns updated object,
  which is needed for GUI and now behave like core update methods.
GUI: improved layout of create resource dialog

- Fixed layout of second page of create resource.
- Shorten inner tab title only for small tabs.
- Remember last selection when refresh on vo/group applications tab.
- Shorter title in rest of small inner tabs.
- Unified naming of tabs for application forms / notifications.
Merge pull request #256 from zlamalp/fixup

GUI: many usability fixes