More Intuitive Remove Collaborator

[zghera]

Issue summary

When editing a trip, it should be intuitive for a user of how to remove a collaborator from the trip.

Expected behavior

The trip editor should be able to click a button that removes that form input box and updates the associated entry in the collaboratorsRefArray state and defaultFormObj.collaborators. Alongside email verification (Issue #67) this should remove the need to check/remove empty fields.

Actual behavior

The only way to remove a collaborator is delete the entry of their email in the input box (change to empty string).