What to do when zocalo finds a centre but does not assign a sample ID

Under certain conditions (see #1038) zocalo may not be able to assign a sample ID to a diffracting centre.

The forthcoming initial implementation in
* #1127

Will not do anything other than log a warning message if such a centre is found.

However since the merge of #1048 there is currently no way for a user to know that a centre was found but not collected, because we do not record the results of the Xrc scan in the comments. There is a list of diffracting centres but it's not obvious if that gives any indication.

At a minimum we need to ensure that this information is easily available.

Perhaps a more advanced handling might make decisions to collect such samples under certain circumstances, and we have some kind of way of post-hoc assigning them to a sample.