Add new information about processing method to perunRequest

 - add endTime and result to perunRequest object
 - change behavior of saving perunRequests, GET will not be saved, PUT
   and POST yes
 - when call ends, save endTime and result to perunRequest if is PUT or
   POST type
 - when some request ends, remove all requests older than defined time
   from list of pending requests
 - set exception to result only if caller throw this exception
CORE,GUI: support for long requests

- Added timestamp mapping for requests.
- Requests are checked on timeout, no message is shown.
- Fixed code indentation.
RPC,GUI: support for long requests

CORE+RPC

- PerunRequest object now contains callbackId, which is sent with every
  callback from GUI (it is timestamp). It's used to address each unique callback.

- Removed sessionId from PerunRequest, since it was the same for all requests
  on one log-in. It was not logged or used anywhere and we couldn't address
  specific request by it.

- Pending requests are now stored in ConcurrentSkipListMap to allow simpler
  addressing by their callbackId.

- GetPendingRequests can send "callbackId" to get specific pending request.
  If parameter is missing, then list of all pending requests is sent back.

- When returning PerunRequest, JSONP serializer ignores perunPrincipal parameter.

GUI

- POST calls longer than 5 minutes display warning about pending request.
  Action in UI continues once all calls are resolved or user can simply close
  the warning confirm.

- GetPendingRequests checks for concrete request, not all and ignores any
  error in order to prevent bloating screen with error messages.

- Updated PerunRequest to match core version.
Merge pull request #618 from zlamalp/stavamichal-perunRequestWithInfoAboutProcessingMethods

RPC,GUI: Support for long requests from GUI
GUI: Added option to force group synchronization

- Added "Force synchronization" button on Group synchronization
  info pop-up.

- Also fixed display of sync. interval when less then 1 hour.
Merge pull request #621 from zlamalp/synchro

GUI: Added option to force group synchronization
GUI: Handle also 403 error code

- When contacting Perun, handle also 403 Forbidden, which happens
  when you have valid session, but with different server or your
  session is expired but browser uses cache.
Merge pull request #623 from zlamalp/forbidden

GUI: Handle also 403 error code
GUI: Proper handling of all HTTP return codes

- Display proper error message on any http return code != 200.
  Our special cases are handled as of until now.
- Code simplification.
Merge pull request #624 from zlamalp/json

GUI: Proper handling of all HTTP return codes
GUI: Fixed display of sync status of groups

- Value in "synchronizationEnabled" attribute is String, so we can't
  just return value from attribute as JSNI boolean. It was wrong in
  conditions but correct on debug message.
- Added some null checks when processing RichGroups.
- Source format of JsonUtils.
Merge pull request #625 from zlamalp/sync

GUI: Fixed display of sync status of groups