[WIP] various fixes

Created by: meguiraun

Hej,

A temporary PR for fixes. Some are only relevant to us (like the prepare_beamline on new sample, in manual mode), and the dc link for non exi.

I found a few bugs with the centring mechanism when several points are on the canvas, point selection has a bug that prevents working with helical under some circumstances (like removing points before), added Cryo, transmission and Mach Info, and default number of snapshot in the mxcollect.xml.

I am doing this PR so you can see and perhaps cherry-pick fixes if you cannot wait, I still need to apply these on master to be mergeable.