luci-base: add L.media() URL construction helper

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit b60b4790d1)

modules/luci-base/htdocs/luci-static/resources/luci.js

@@ -1748,6 +1748,28 @@
 			return this.path(this.env.resource, arguments);
 		},
 
+		/**
+		 * Construct an URL path relative to the media resource path of the
+		 * LuCI ui (usually `/luci-static/$theme_name`).
+		 *
+		 * The resulting URL is guaranteed to only contain the characters
+		 * `a-z`, `A-Z`, `0-9`, `_`, `.`, `%`, `,`, `;`, and `-` as well
+		 * as `/` for the path separator.
+		 *
+		 * @instance
+		 * @memberof LuCI
+		 *
+		 * @param {string[]} [parts]
+		 * An array of parts to join into an URL path. Parts may contain
+		 * slashes and any of the other characters mentioned above.
+		 *
+		 * @return {string}
+		 * Returns the resulting URL path.
+		 */
+		media: function() {
+			return this.path(this.env.media, arguments);
+		},
+
 		/**
 		 * Return the complete URL path to the current view.
 		 *

modules/luci-base/luasrc/view/header.htm

@@ -18,6 +18,7 @@
 <script type="text/javascript">
 	L = new LuCI(<%= luci.http.write_json({
 		token          = token,
+		media          = media,
 		resource       = resource,
 		scriptname     = luci.http.getenv("SCRIPT_NAME"),
 		pathinfo       = luci.http.getenv("PATH_INFO"),