Implement collection form features to trip form

[mikkohei13]

As someone using Vihko to manage personal collections, I want to have features needed for collections, so that I save time and can enter better data.

1. Show depth field on Gathering level, not visible by default, after height field

https://schema.laji.fi/property/MY.depth

2. Show unit id's on the form

This is probably implemented on dev collection form, but cannot check since saving the form fails due to habitat field errors: https://dev.laji.fi/project/JX.5190/form