As we can no longer go to settings singletons, the Qt application should
rely on properties on settings proxies. Adding a helper signal on
pqServer to notify the world that some settings proxy has changed.

pqFiltersMenuReaction: now works in client-server mode

See merge request async/paraview!82

Skip "Apply" on uninitialized objects.

See merge request async/paraview!81

Server connection

See merge request async/paraview!79

Apply should be emitted only on objects that have completed the initialization phase.

Adding ability to unregister services/endpints.
vtkClientSession/vtkServerSession now ensure the services and endpoints
are unregistered in the destructor.

vtkPVRenderView: fix camera clipping range

Closes #35

See merge request async/paraview!78

Ensure that vtkPVRenderView's clipping range is setup correctly.

Disable properties panel until proxy is ready

See merge request async/paraview!77

This commit disables the property panel of a proxy until it is ready.
This allows to initialize the properties panel without  having to deal with
cases where the panel was modified before the proxy was ready.

vtkThalliumRunLoop: avoid busy waiting for tasks

See merge request async/paraview!76

vtkThalliumRunLoop was using default scheduler which caused the run
loop to use a busy wait. This was causing the CPU to be pegged to 100
even when no work was being done. Fixed that.

Load state

See merge request async/paraview!75

This reverts commit 8c21864a.

Point .gitmodules to async/vtk

See merge request async/paraview!74

enable "Recent Files" menu

See merge request async/paraview!73

Refactor vtkSMReaderFactory.

See merge request async/paraview!72

vtkSMReaderFactory is now held by vtkClientSession. Also simplifying
reader factory to no longer do "CanReaFile" checks. Those checks are not
universally supported by readers anyways. Let's remove them for now, we
may reintroduce that behavior in the future.

color palettes and interaction styles

See merge request async/paraview!71

This helps us avoid pushing properties that don't have any effect on the
services.

Had to refactor how interaction styles are handled since we can no
longer do them in vtkPVRenderView. These are no explicitly handled by
vtkSMRenderViewProxy.

Cleanup settings loading/saving

See merge request async/paraview!70

* user settings are all now placed under a directory that using the app
  name alone (organization is largely silly for our use-cases)
* qt settings are saved in a file named `qt-${version}.ini` while
  sm-settings are saved in a file named `user_settings.json` and
  `site_settings.json`.
* user-settings are now saved/loaded as expected by client applications
  alone.