* Miscellaneous cleanup of typos + change some return types for IDE helpers
* Call/use parent::__construct() to add filters for settings output, saving
* i18n: simpler translation strings
* i18n: simpler translation strings
* i18n: readble printf(), and moving the %s placeholder to `%s product`
* i18n: make string translatable and remove the HTML tags
* i18n: avoide using HTML tags in translatino strings
* Fixed case for all _e, esc_attr_e and esc_html_e strings
* Fixed case for all _n_noop strings
* Fixed case for all _x strings
* Fixed case for all __, esc_html__ and esc_attr__ strings
* Fixed a few more strings
* Fixed strings in unit tests
* Fix PayPal Standard case.
* Save Order text
* fixed indentation - swapped spaces for tabs at start of line, swapped
tabs for spaces min-line for alignment
* removed instances of `@return void` and `@access public`
* improved readability
@see http://make.wordpress.org/core/handbook/coding-standards/php/