Server Settings already has a Custom Headers editor, so adding one to the
manual add form created a second place to edit the same field. The reporter
had also conditionally withdrawn #1915 — "editing that information from the
server settings dialog is sufficient" once #1848 closed, which it has.
Reverts the add-form editor, the shared KeyValueRows element, the optional
`settings` argument on addServer / updateServer, and the App-level merge
helper. What remains are two defects found while working in
ServerSettingsForm, which this PR now closes instead (#2040): the Custom
Headers hint misstating OAuth precedence, and the key/value rows' missing
accessible names.
Signed-off-by: cliffhall <cliff@futurescale.com>
4dd8ed4498