Allow setting multiple values to a property

[shgysk8zer0]

Using the _set method only allows for setting a single value. Need to create an _add method that will append values to an array (or SplObjectStorage).

Will then need to add appropriate methods such as Thing::addImage() and update database structure to allow jsonb[] storage.

[shgysk8zer0]

Need to update JSON encoding of multiple values. They are not having @type set.

[shgysk8zer0]

Will also need to:

• Update save method to handle multiple values as jsonb[]
• Parse results from SELECT queries