fix the issue with edit boxes losing input on the metadata page by using our full database metadata endpoint to load all our necessary information at one time.  part of the underlying problem is that we were looping over the tables to get the metadata and each time the data updated we re-rendered our form and it would clear existing input, so while loading was happening it was easy to lose your input.

consolidate all of the angular API service code into the main services.js file.  we were mostly going this route already, but this just makes it simple and puts all the api code in a single place.

remove code around connection testing from frontend database create/update now that it is being handled in the api.

fix issue where database create/update was still trying to call the db_form_input endpoint which we removed recently.

provide information about our `:engines` through our main MetabaseSettings which simplifies some things and removes the need for a /api/database/form_input endpoint.

apply the same basic logic and styling to the Data Reference section for FK connections that we just added to the object details page.

tighten up the styling on the connection "via" span and update logic to only show the path of the FK relationship is needed (aka if there are multiple references from the same table)

add a function in our schema metadata lib for `foreignKeyCountsByOriginTable` which counts the occurrences of FK relationships by the origin table they come from.  this allows us to know if a given origin table is represented multiple times in a list of FKs.

provide an indication of the FK field that was used to determine the connection on object details relationships pane.

Mostly working conversion of database edit/create to React. Also incorporate some of the UX improvements (delete confirm, animating FormMessage)