If the viewport height is smaller than 660, shrink the margin above &
below the telemetry modal.
If the viewport height is smaller than 540, also remove the image banner
at the top of the telemetry modal.

This indicates the current state, lets the user exit without changing
state, and lets the user change state any time they want.

This change also improves RTL support in the telemetry modal.

If `onClickAbout` is a callback, or is not provided, then behavior is
the same as it was before this change. If the value is an array of
objects with `title` and `onClick` properties, the "About" button will
now open a menu with those items.

TODO: support `FormattedMessage` for the menu item titles.