Don't show empty repeat instances

[lognaturel]

It can sometimes be helpful to make the entire contents of a repeat instance non-relevant: #137 (comment)

In that case, it's helpful for the repeat instance to be entirely hidden. Remaining repeat instances should still be numbered according to their position with the hidden instances. For example, if there are 5 repeat instances and only the 2nd and 4th have contents, they should be the only two instances visible and should have numbers 2 and 4. See the linked Enketo issue for a screenshot and a description of the desired behavior. Collect also does this.

[lognaturel]

Sample form that shows the pattern:

household_listing.xlsx

We prefer doing this over having the second repeat use a repeat_count of the number of members under a certain age because this pattern is resilient to changes to the initial household roster. For example, if a member gets deleted after some children have been processed, the data submitted is still coherent.

[lognaturel]

@sadiqkhoja has come up with another variation on this theme where all fields in a repeat are calculates so there are no visible body elements.