Remove :all_columns and :all_associations options

They allow for insecure behavior, and only exist for backwards
compatibility.
Remove Model.json_create

This only exists for backwards compatibility when the JSON.parse
:create_additions=>true option is used.  Such usage is insecure,
and it depends on the :all_columns and :all_associations options,
which are being removed, so it needs to go as well.
Integrate many_to_one_pk_lookup plugin

When this plugin was originally added, it did not handle as many
corner cases as it does now, so integrating it would likely have
broken things.  With recent changes, I think the approach is
robust enough to use by default, and it has definite performance
advantages.
Integrate association_autoreloading plugin

This plugin causes a minor performance hit on the column setters,
but the cache really should be cleared if you change the column.