Error messages aren't displaying on the remote container create form

[MilanPospisil]

https://issues.redhat.com/browse/AAH-1845

This PR refactors error handling using utils. Every error (including field validation and server side validation together) is now in one associative array formErrors, which can hold error message per form field (for example formErrors['name']).

Also, validation from server in attempt to save the form is now included.

[himdel]

This is missing a PR description now, what is this supposed to do? :)

[himdel]

One more thing noticed during testing... this doesn't deal with unknown errors from the server in any way, no alerts, no messages, just a stuck form.

Try adding a EE with a name like foo/. - this passes the name validation, but the server responds with a base_path validation message .. we should be displaying unknown messages on error.
(Though maybe as a usability improvement, this should be also associated with the name field, so that onChange can unset it.)

(The response looks like...

{
  "errors": [
    {
      "status": "400",
      "code": "invalid",
      "title": "Invalid input.",
      "detail": "The provided base path contains forbidden characters.",
      "source": {
        "parameter": "base_path"
      }
    }
  ]
}

)

[MilanPospisil]

TODO - delete validation errors when alert is shown and error does not belong to any field.

[himdel]

Looks like this works 👍

(just needs a rebase to get tests green, #3018 )

[himdel]

👍 (once tests go green)