Update remote_website_install.sh: Another boatload of changes

* DIALOG_WIDTH is now determined based on the width of the window.
* Don't display DIALOG_BACK_TITLE - I found it confusing looking.
* Replaced display_info_box() and display_prompt_dialog() with calls to display_box().
* Cleaned up some DIALOG_TEXT's.
* Make the pre-checks dialog box more dynamic.
* Only check for remote config file (new or old) if we found a remote Website.
* Warn the user if a remote config file was found on the Pi but no remote Website was found.  Not sure what the file would be for.
* Improve checking if mirror worked.
* Don't display the "Overwriting old file ..." entries - they make it hard to read the output.
* Use "--no-perms" to avoid "chmod errors".
* Temporarily disable the remote Website before uploading to avoid conflicts.