Sharing calibrations across xma files

[elska_kaczmarek]

An xma file allows you to have one set of calibration images, and then add multiple trials that were taken at the same time. In a discussion with other xromm users, we realized that most of us don't use this feature, i.e. having multiple trials in the same xma file (or at least not in the way it was intended). Instead, for various reasons, many of us have different xma files for each trial, but then it becomes hard to try to have the calibration be the same across these files. 

A proposal for a new feature is either a way to have multiple xma files reference a different (xma) file for their calibration (so that changes to the calibration would automatically ripple to the downstream xma files), or the ability to import a calibration from another xma file (so that if you change the calibration you can import it into all xma files that use that calibration).

[Benjamin Knorlein]

I added a load trial button which can load a 2nd xma-file for the calibration. This was the easiest and the most efficient as the new calibration can be set during opening the xma-file.

[Benjamin Knorlein]

fixes #219 : Added an option to load an xma-file with the calibration of another one

→ <<cset 3d7147fef3f5>>