CORE, RPC, GUI: very raw version of new user detail for internal testing

GUI:

- User can switch his identities by "select identity" option in menu.
  If have only one, option is disabled. Switching still can be done
  through service identities table and associated users table.
- User can update titles in name from GUI.
- Perun admin can update whole user's name from GUI.
- User can see his certificates with expiration date.
- User can change password or go to reset gui from Authentications tab.
- User can change preferred email, language and timezone.
- On service identity detail user can change its email or add new login
  (if supported namespace) and set password. Login can be added only if
  there wasn't any before (proper checks are in core method addLogin()).

- Perun GUI can be used to display mail change verification results.
- Added new callbacks, updated User object, removed unused classes.
- Better error message formatting (proper width) for "Extended" input widgets.
  Also can display HTML and not just the text.

- Added test tab for JSON parser for further testing. Parsing simple
  values like string, integer works locally but not in production runtime.

CORE, RPC:

- Multiple small fixes of typos.