Have Gen2 exposure command calculate estimated time more precisely.

During SuNSS observation, estimated time for sps exposure was too conservative (~100 sec longer than actual duration), because overhead was set for PFI lamp exposure. We need to calculate duration of PFI lamp and science exposure (and else) separately.

Also. it is nice to show how many frames are taken so far. Since the number of frames is controlled PFS internally, we may need to find a way to monitor the created frames..