Remove all frameworks except Bootstrap (#251)

- Remove all frameworks except Bootstrap

- Remove roots-options.php and replace with a more simple
  roots-config.php

- Include all Bootstrap Javascript plugins by default in
  js/plugins.js

- Use Bootstrap Responsive and Topbar navigation by default

- Use Bootstrap markup on forms, page titles, image galleries,
  alerts and errors, post and comment navigation

- Remove Roots styles from style.css and introduce app.css for
  site-specific CSS. Remove almost all previous default Roots
  styles.

- Add latest updates from H5BP project

css/less/grid.less

@@ -0,0 +1,8 @@
+// GRID SYSTEM
+// -----------
+
+// Fixed (940px)
+#gridSystem > .generate(@gridColumns, @gridColumnWidth, @gridGutterWidth);
+
+// Fluid (940px)
+#fluidGridSystem > .generate(@gridColumns, @fluidGridColumnWidth, @fluidGridGutterWidth);