v3.1.5: Bugfixes

This release contains changes associated with the following GitHub issues:

#84: Adding language-translation for Back to Top button's title= tag.
#85: Adding alt= tag to additional images.
#86: Adding aria-label and -title to shopping-cart buttons.
#88: Correct form-start tag placement to correct invalid HTML on checkout_confirmation.
#89: Correct data-overflow on account page's Previous Orders.
#91: Correct PHP notices issued when left/right columns are fully disabled.
#92: Enable integration with attribute image-swapper plugins.