WooCommerce API Manager 3.3.4

* Fix: Only load Storefront My Account CSS if Storefront is the selected theme.
* Fix: PHP warning if api_key value not sent in request for API Information and Update functions queries when the product_id value is a legacy Software Title string.
* Tweak: Minimize CSS files.
* New: Added database caching option to settings.
* New: When enaabled, cache some data for Order screen, and My Account tabs: API Keys and API Downloads.
* New: When enaabled, cache data for API functions: status, information, and update.

* Fix: Fixed several errors in get_api_information_and_update_product_id() method that caused legacy Software Title string API update function queries to fail.
* New: If 'version' key and value are sent in query string to 2.x API functions activate, status, information, or update, or legacy pre 2.0 API functions plugininformation, or pluginupdatecheck, the 'version' for an API Key activation will be updated in the 'wc_am_api_activation' database table.

* Fix: 'slug' requirement in API Update function removed, as it could cause pre version 2.0 clients to have failed update request.
* Fix: Software Title on Product edit > API tab can no longer be updated, as it was deprecated at version 2.0.
* Fix: Incorrect product_id was found if the client sent a legacy Software Title string, rather than the new numeric value for the product_id to the API Update function. This caused legacy API Update requests to fail, particularly for Variable products.
* New: Added Requires PHP version data option to the WordPress plugin information API.
* New: Requires PHP version field added on the Product edit API tab, and Variable product variation settings.
* New: Added icons to product API tab.
* New: Added My Account dashboard API Keys and API Downloads tab icon when using Storefront theme.
* New: Added 'wc_api_manager_update_active_required_keys' filter to API Update function.