added bootstrap-switch

- updated package.json
- updated build/npm/Plugins.js
- added build/scss/plugins/_bootstrap-switch.scss with bootstrap 4 style & color overrides
- updated pages/forms/advanced.html with bootstrap switch demo & added rows in icheck demo
- added plugins files

package.json

@@ -56,6 +56,7 @@
     "bootstrap": "^4.3.1",
     "bootstrap-colorpicker": "^3.1.2",
     "bootstrap-slider": "^10.6.2",
+    "bootstrap-switch": "^3.4.0",
     "bootstrap4-duallistbox": "^4.0.1",
     "chart.js": "^2.8.0",
     "datatables.net": "^1.10.19",