Add the ability to add a new gift idea to a birthday

FIXME: The page needs to be refreshed manually for the list to be
updated
Merge pull request #25 from sebn/add-gift-idea

Add the ability to add a new gift idea to a birthday
WIP: Set up birthday person change UI (not core)
Create feature function skels
Change person, but still show the old description
Fix core/birthdays tests to enfore birthday person
Ensure all birthday properties are stored
Update birthday description on person change
Birthday person creation & change