Feature/implement blueimp namespace for angular

This PR adds the `blueimp` namespace to the AngularJS directives as recommended by the AngularJS team to avoid naming conflicts with other third party directives (especially names like `progress` and `preview`).

The changes only impact the code related to AngularJS and the corresponding example has also been updated and tested locally.

Example:
`<div data-progress>` is now refactored to `<div data-blueimp-progress>`
`<div data-preview>` is now refactored to `<div data-blueimp-preview>`