[IMP] website_theme_install: optimize animation

Following commit 828c7c3da9:
the kanban record animation when a theme is hovered was blurry with
chrome and laggy with firefox (with linux at least). This commit
removes the scale part of the animation which was the cause of this.

addons/website_theme_install/static/src/less/website_theme_install.less

@@ -96,7 +96,7 @@
         &:not(.o_theme_installed) {
             .o_theme_preview_top:hover {
                 .o-transition(all, .3s);
-                .o-transform(scale(1.0125) translateY(-5px));
+                .o-transform(translateY(-10px));
                 border-color: darken(@o-theme-kanban-gray, 26%);
                 box-shadow: 0 15px 12px -8px rgba(0, 0, 0, .4);