* Move tny_folder_sync after remove operation and define it

on modest-ui-actions, when all messages have been removed.
* Review progress-bar widget to get more information when
undetermined data is come back from camel-operation.
* Move header_view_refilter operation, defined in
folder_monitor_update to main_window, which is an observer
of headers view. Sometimes, refilter operation was done before
model was updated, causing several crashes.

pmo-trunk-r2915