Rework copy to clipboard code into a namespace ensemble object.
Modify view dialog to make URL, username, password, and notes fields perform
copy to clipboard upon double click.
Fix bug in new view entry double click to paste code when run under
Windows (and likely MacOS as well).

Add a call to clipboard clear/append for X11 (likely unnecessary, but
no harm if so).

Remove three stray debugging puts from sha256.tcl.
Add code to simulate an X11 like copy-upon-select operation to the
notes widget in the view login window.
Change view window text widget to use "-exportselection false" mode,
which prevents double activation of the copy operation on Windows.
Merge branch 'view-dialog-mods' into pre160

Enable clipboard copy-paste-action in the view-login-dialog