Support scripting list of images

[albireox]

Observers often want to expose several time on the same object using different exposure times and filters. Right now they have to do that manually waiting for each image to finish. It would be good to support some form of scripting. This could be just a text box in which the observers write the exposures they want to take using some format, and the webapp interprets them and sends them to the server sequentially. For example

5 object r 60
1 object ha 180
2 object g 300

which would take 5 "object" images in the r band of 60 seconds each, one 180 s image in H-alpha, and 2 g-band 300s images.

The feature should clearly show which exposure is being taken and allow to abort the sequence if necessary.