capture.cpp: exposure changes
capture.cpp: exposure changes

* Use more accurate timeToTakeImage_us values, based on additional testing.
* Changed aggression to 75% so changes would happen quicker.
* Fixed typo
* Improved a comment.
* Used aggression for images that didn't use histogram exposure algorithm (e.g., night) to hopefully dampen the flickering when the moon is out.
* Removed statement to set `current_exposure_us = last_exposure_us` when manual exposure is set since those values are the same.
thomasjacquin/allsky,thomasjacquin/allsky,thomasjacquin/allsky