Check for samples in assays further in assay stream when creating an in-between assay.

[NielsGeudens]

It is now possible to add an assay between two existing assays, providing the next assay does not contain samples. When having samples in the next assay, it provides an error when trying to add an in-between assay, as it should. (coded in #1656

However, when deleting the samples in the next assay (n+1) (thereby breaking the link with the assay further down (n+2), it does allow to insert the assay at position n. The user might think this is an 'okay solution' by first deleting the samples at assay n+1, then making the additional assay (position n), and then making samples again in assay n+1. However, the id of the samples will of course be different, and no longer linked to assay n+2.

is it possible to check the presence of samples in the assays further downstream rather than only in the next assay, and forbidding the creating of an in-between assay if any of the following assays contain samples?