Partially fixes NB#78521

Partially fixes NB#78521
  * src/maemo/modest-progress-bar-widget.c:
    When the progress bar receives a "progress-changed" signal from its mail operation
    where state->done = 0 and state->total = 0, it begins to pulse periodically until
    the mail operation finishes or it receives a "progress-changed" signal with
    positive values.
    * (modest_progress_bar_widget_is_pulsating) :
    * (modest_progress_bar_widget_set_pulsating_mode) : manage this pulsating mode

* src/modest-mail-operation.c
    * (modest_mail_operation_update_account) :
    * (modest_mail_operation_get_msg) :
    * (modest_mail_operation_get_msgs_full) :
    * (modest_mail_operation_refresh_folder) : these functions send an initial "progress-changed"
        signal because it could happen that the first signal with "real" data takes a long time
        to happen, or in some cases doesn't happen at all, leaving the user with an empty
        progress bar for a while.

pmo-trunk-r3912