Reverting to Yii2 bootstrap 2.1

A ill-fated attempt was made to divorce from yii2 components

Navigation is 100% Yii generated

Instead of requiring user to install bootstrap 4 version of yii-bootstrap, i added the bower asset requirement to the composer.json.

I've also developed a NavBar and Nav based on the Yii2 components of the same name, with additional functionality for bootstrap 4 and for an accordion style submenu apropos of this template.

1st release

This release has a working Yii2 layout that is visually indistinguishable from the original, but with navigation produced via yii\bootstrap\Navbar & yii\bootstrap\Nav.