Support for VoObserver role + usability and design fixes in GUI

CORE:
- Added privilege to list vo's groups and vo/resources tags to VoObserver.

REGISTRAR
- Added privilege to list applications of VO/Group/Member to VoObserver.
- Added authz for getting application form items.

RPC:
- Registrar interface changes (pass session).

GUI:
- VoObserver can now browse all tabs like vo admin, but all buttons
  and table checkboxes should be disabled.
- Tabs for add/assign/edit are not accessible for new role.
- Added new method to JsonCallbackEvents which can be used to pass data
  (results) from one callback to another.
- Display custom messages in empty tables (e.g. when no VO has no groups) and also
  display custom text when filtering/searching returns 0 results.
- Fixed display of application form items table (table now looks like other tables)
  and remove unnecessary border in form item widgets made of tables. 
- Added filtering above facility resources by resource name or vo name/shortName.
- Added filtering above Tasks (by service/type) on facility detail.
- Fixed menu refresh on PerunAdmin/Facilities tab.
- Source formatting, fixed typos.