Support multiple collections for add function

[mohammadKhalafi]

issue : https://github.com/mavoweb/mavo/issues/829

[mohammadKhalafi]

Hi there, thank you so much! Maybe it's that I've just woken up, but i found it hard to follow the logic. Some comments would help, especially around L106-113

Hi! a few comments is added.

[LeaVerou]

Thanks! At a quick glance it looks alright, though I haven't tested it or done a deep dive.

@DmitrySharabin could you take a look as well? Note this question I raised in the original issue:

One question is: What do we do when some items in an array belong to collections and others do not? Do you add to those collections, or do you give up altogether?

[DmitrySharabin]

Hey there,

Sorry for the delay. I played a bit with the suggested changes. And it looks like the generated Add <collection> buttons (framed in the screenshot) stopped working.

@mohammadKhalafi You may find these tests useful for debugging: https://test.mavo.io/actions.html#add. And could you please provide a test case on Codepen so it is obvious how the new feature will work?