Stackable Premium

* New: Added new Aspect Ratio option to Image block and relevant blocks #3200 * New: Added filter stackable_force_css_load - when returning true, Stackable css files will always be loaded in the frontend even if no blocks are present #3218 * New: Accordion block - accordions show open when printing the webpage #3186 * Fixed: Posts block - empty excerpts may show some excerpt markup #3185 * Fixed: Posts block - excerpt length not being followed #3210 * Fixed: Load more block - clicking rapidly can load the same posts #2280 * Fixed: Accordion block - prevent highlighting text when toggling #3096 * Fixed: Accordion block - some icons in the content rotate when opening the accordion #3211 * Fixed: Table of Contents block - excluding headings can affect another TOC block in the same page #3197 * Fixed: Inner column block - top and bottom margins looks different in Firefox #3193 * Fixed: Some CSS validation errors #3087 * Fixed: Some custom SVG icons may not display properly #3103 * Fixed: Image blob shapes sometimes look different in Firefox #3042 * Fixed: Nested selectors in Custom CSS now work properly #3164 * Fixed: Security improvements