BUG #14663: Add indicator for num-of-timesteps in toolbar.

If a dataset with timesteps is opened, the toolbar that allows user to
select the timestep now also shows a label next to it with the number of
timesteps in the data.

Change-Id: I1af7780c938f3213392156f685b3149cde045142
Merge topic '14663_timesteps_indicator' into next

b09b0895 BUG #14663: Add indicator for num-of-timesteps in toolbar.