v4.0.0: Releasing as an encapsulated plugin

This version contains changes associated with the following GitHub issues:

#35: Now distributed as a Zen Cart encapsulated plugin, for zc158 and later.
#26: Add customers_email_address as an optional column for "Orders Line-Items" reports.
#36: Using the Zen Cart admin_html_head.php to load required CSS/JS files, each now as their own file.
#37: Correct 'matrix' display, was using products id, not uprid, so attributed-products weren't properly displayed.
#38, #39: Various refactorings and performance improvements.
#40: Adding "Last 12 Months" as a preset date selection.
#41: Use "datepicker" instead of "spiffyCal" for custom-date selection.
#42: Change DISPLAY_EMPTY_TIMEFRAMES constant interpretation; true now displays the timeframes (was false in previous versions of the report).
#43: Enable additional order-total discounts and surcharges via site-specific customization.