Draft: multi instance imageviewer

Allows multiple instances of the 2dview component to be rendered in the same layout. To do this instances are now constructed from a named list of sources. One source can now be designated the sample_origin, i.e. relative to which samples, subsamples, images, etc are marking. Many can be origin to which the beam is marked.

This also allows adding and updating markings. These were previously only the beam, but now can be generic marks with names as well. In order to save markings daiquiri needed to support saving out yaml as well as loading it.

Yaml saving moved to !445 (merged)

UI side of the work is in daiquiri-ui!301 (closed)