ECalClient: Create view objects in the D-Bus thread.

ECalClient: Create view objects in the D-Bus thread.

Flip-flop the sync/async implementations.  The view object should be
instantiated from the dedicated D-Bus thread so its underlying proxy
object shares the same main loop context as the client's proxy.

Have the view object schedule idle callbacks on the client object's
main loop context to emit change notification signals, so as not to
expose the dedicated D-Bus thread to external signal handlers.