driver andorcam3: look for libatcore.so if libatcore.so.3 is not present

the default Andor installation only installs libatcore.so, so accept it too, even if it's not
recommended on Linux.
driver andorcam3: don't wait too long between frames

as the camera automatically starts the next frame acquisition, the time to wait for the next frame
can be less than exposure time + readout time. So waiting that long was constantly adding
a delay, that kept building up until the SDK queue was full. Instead, we just wait for the next
frame immediatly.

also add setup to read metadata (=timestamp), which is what allowed to detect the problem
driver andorcam3: improve acquisition speed and ensure settings are fixed

Small tweakings to improve acquisition speed.
It will still fill up the hardware queue if the frame rate is too high.
So far the tentatives to handle full hardware queue in a simple way failed.

Fix shutter to global, as it ensures all the pixels show the same thing at the same time.

Also explicitly set the framerate to the maximum. It seems that with the Zyla USB, sometimes
it remembers the old framerate, which is counter intuitive for the user.