Remove unnecessary, hard-coded json builders
Rename type field to asset_type

Rails magic uses "type" to mean a very specific thing.  Not _type or "internal_type" or something
sane, just "type".  Oh, and it doesn't tell you it's magic until you actually SET it.
Fix error when trying to build "type" select

Rails internally reads the form object's data even when specifying
an item to have pre-selected.  To avoid likely collisions, the form
field has been changed to be identified by __magic_type, and the
form's object is hacked in-place to return an empty string when that
method is called.
Merge branch 'remove-type-field'