Added button and action to keep place
in adWebview -- button action calls
a Javascript functon (keep_place())
in the WebView --- in the loaded
web page.
SUCCESS! Introduction of the delegate method didFinishLoadForFrame
in AppDelegate.swift now implements the sought-after
live keep-in-place feature for WebView content.

The delegate method calls keepPlace(), which in turn
executes the Javascript keep_place, the definition
of which was inserted into the source file by
the function preprocessFile(filePath).