[fix] simple theme: make JS sources available on non build hosts

Include the source files directly in the `.map` files [1] for two reasons:

1. In the simple theme, modules from `./node_modules` are only available on
   developer's build host (a `make node.env` is needed to get the sources).  By
   example; in the `searxng.min.js.map` file, the `autocomplete.js` is linked at
   URL:

      ../node_modules/autocomplete-js/dist/autocomplete.js

2. Later, when client sources has been moved out of the `./static` URL [2] to
   the `<repo-roo>/src` folder, all JS sources are no longer available.

Drawback: `.map` files grow up in size, but this should not bother, because the
files are only loaded in debug mode.

[1] https://github.com/gruntjs/grunt-contrib-uglify#sourcemapincludesources
[2] https://github.com/searxng/searxng/issues/141

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/static/themes/simple/gruntfile.js

@@ -88,7 +88,9 @@ module.exports = function(grunt) {
         warnings: true,
         compress: false,
         mangle: true,
-        sourceMap: true
+        sourceMap: {
+          includeSources: true
+        }
       },
       dist: {
         files: {