Improve dataTables integration within the app:

- Manage lib through NPM
- Move portal / Bootstrap files back to the itop-portal-base module (not managed through NPM yet)
- Fix SCSS classes for the backoffice as it was based on the bootstrap CSS classes which are not there anymore

Note: jQuery is included as a dependency, will check with the team if we can force it not to be retrieved

node_modules/jquery/src/var/flat.js

@@ -0,0 +1,16 @@
+define( [
+	"./arr"
+], function( arr ) {
+
+"use strict";
+
+// Support: IE 9 - 11+, Edge 18+, Android Browser 4.0 - 4.3 only, iOS 7 - 11 only, Safari 11 only,
+// Firefox <= 61 only
+// Provide fallback for browsers without Array#flat.
+return arr.flat ? function( array ) {
+	return arr.flat.call( array );
+} : function( array ) {
+	return arr.concat.apply( [], array );
+};
+
+} );