[FIX][UI/UX] Theme Customizer: close translation tag and hide generate LESS button (TODO: convert the pref to support SCSS)

There was a problem with the translation tag tr witch was not well closed, and there was also the button to Generate custom Less code that was not working (no action attached) but the logic has been develloped, so the solution was to hide it until decision to re-introduce on future version of tiki, to have a better the documention. Related task: https://avan.tech/item72808-Review-https-doc-tiki-org-Theme-Customizer-feature-and-documentation