This commit introduces a new PHP file `icons.php` that defines a set of inline SVG icons to replace the Bootstrap Icons webfont. The icons include common UI elements such as calendar, clock, folder, and tag, as well as theme picker icons like sun, moon, snow, droplet, cup, and half. The SVGs are designed to scale with existing font-size rules and are accessible via the `blowdit_icon` function. Additionally, a mapping function `blowdit_theme_icon` is provided to associate theme keys with their corresponding icon names.
