Add grunt.js build script

- Move Bootstrap LESS files into new subdirectory

- Change app.css to app.less, add @import's to utilize
Bootstrap variables and mixins

- Remove plugins.js and main.js

- Move Bootstrap JS plugins into new subdirectory

- Add new _main.js file with example DOM-based routing
script that works off the WordPress body_class

- lib/scripts.php has been updated to remove all extra
CSS and JS files and also places JavaScript in the footer

assets/css/less/app.less

@@ -1,3 +1,12 @@
+/*!
+ * Roots 6.1.0
+ */
+
+@import "bootstrap/variables.less";
+@import "bootstrap/mixins.less";
+@import "bootstrap/responsive-utilities.less";
+@import "bootstrap/utilities.less";
+
 /* ==========================================================================
    Base
    ========================================================================== */