v3.6.0: Bugfixes and additional colors

This release contains changes associated with the following GitHub issues:

#236: Restructuring and notifications added for AJAX search.
#237: Add missing language constant for AJAX search.
#238: Add a 'soft' configuration setting to disable the 'back-to-top' icon.
#240: Simplify and reduce processing for SNAF pages.
#241: Price-related observer updated to honor a previous observer's changes.
#244: Add a 'soft' configuration setting to control whether zca_js_zone_list returns zone_id or zone_name values.
#245: Correct name of "Add Address" button on the address_book page, was displaying as "Back".
#246: Add role="button" to AJAX search header link to improve SEO rating.
#247: New colors defined for upper NavBar buttons (other than the AJAX header search icon).
#252: "Images" column for table-based product listings updates for screen-readers.
#253: Colors added for "Advanced Accessibility Standards". See this (https://github.com/lat9/ZCA-Bootstrap-Template/wiki/ZCA-Bootstrap-Stylesheets-and-Colors#v360-updates) link for details.
#254: Correct styling for "Buy Now" buttons, 'more info ...' link and min/max/unit display on table-based listings.
#258: ask_a_question and account_history_info page/template updates based on recent zc158 base changes.
#259: Correct HTML validation issues on additional-images' modal display.
#261: "Sold Out" button, add coloring and remove hover-pointer since the button's not clickable.
#266: "Float" the 'Add Selected to Cart' button on product listing pages, to keep the button visible in the customer's viewport.