Add inline SVG icons for UI and theme picker

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.

php/page.php

@@ -18,8 +18,8 @@
 		<?php if (!$page->isStatic() && !$url->notFound()): ?>
 		<!-- Creation date, reading time and author -->
 		<div class="metadata mb-4">
-			<span><i class="bi bi-calendar3"></i><?php echo $page->date(); ?></span>
-			<span><i class="bi bi-clock-history"></i><?php echo $L->get('Reading time') . ': ' . $page->readingTime() ?></span>
+			<span><?php echo blowdit_icon('calendar'); ?><?php echo $page->date(); ?></span>
+			<span><?php echo blowdit_icon('clock'); ?><?php echo $L->get('Reading time') . ': ' . $page->readingTime() ?></span>
 		</div>
 		<?php endif ?>
 
@@ -43,11 +43,11 @@
 		<div class="post-taxonomy mt-4">
 			<?php if ($categoryKey) : ?>
 				<a class="taxonomy-badge" href="<?php echo $page->categoryPermalink(); ?>">
-					<i class="bi bi-folder2"></i><?php echo htmlspecialchars($page->category(), ENT_QUOTES, 'UTF-8'); ?>
+					<?php echo blowdit_icon('folder'); ?><?php echo htmlspecialchars($page->category(), ENT_QUOTES, 'UTF-8'); ?>
 				</a>
 			<?php endif ?>
 			<?php foreach ($tagsList as $tagKey => $tagName) : ?>
-				<a class="taxonomy-badge" href="<?php echo DOMAIN_TAGS . $tagKey; ?>"><i class="bi bi-tag"></i><?php echo htmlspecialchars($tagName, ENT_QUOTES, 'UTF-8'); ?></a>
+				<a class="taxonomy-badge" href="<?php echo DOMAIN_TAGS . $tagKey; ?>"><?php echo blowdit_icon('tag'); ?><?php echo htmlspecialchars($tagName, ENT_QUOTES, 'UTF-8'); ?></a>
 			<?php endforeach ?>
 		</div>
 		<?php endif ?>