Nix FieldTypes routes and just send plugin slugs to HTML template

Also don't load plugin twice. This makes the current "Location" FieldType only available when the module is installed.
Small form improvements

Move instructions below label, and default tabindex to 1 (to create our own flow within a form)
Fix for input

Was sending an object if an empty string, etc., just needs existential check
Improve field input views for EntryEditView

* Guarantee field order by always rendering a field first, then re-rendering if a plugin is loaded.
* Render an error if field type is not default and a plugin can't be found
Revert to simpler test loading

Too fancy