gui acq: small test cases improvements
gui acq: rename startAcquistion to acquire()

simpler is better
gui acquisition: avoid the time left estimation to go backward

It's confusing for the user, and it's still just an estimation anyway.
So only allow the estimation to go backward if the new one is really different.
gui acq: save file in a separate thread after acquisition.

This allows to not block the whole GUI while the file is being saved.
andorcam2: add info from Andor about EMCCD gain

"I've tested this with an Ultra here and have reproduced your issue.  Real gain should be selectable using SetEMGainMode(3), this is the case for iXon3 which has the same sensor.  So I have raised this issue with the Ultra/SDK team. Linear gain is very similar to RealGain.  The main difference is that it does not compensate for EM Gain aging. For now this should give you similar results until I get some more information from the Ultra/SDK team."
gui acq: also ensure the gauge doesn't go back
model: fix problem with progressive future estimate at start
gui stream: clean up