Change Event-ReturnEvent relation from ManyToMany to OneToOne.
Fix return_date validation issue when creating new return event.

The current date created for comparison was too populated, needed to
create one with only year, month and day set.
Refactor a bit and add docs to javascript functions.
Create style for textarea objects.
Add title for outdated invoices badge.
Prevent events from being moved to date that is earlier than current date.