Add task to load specific dependencies from cdn

[maxklenk]

While working with the local file when developing, I would like to be able to specify dependencies which should be loaded from a cdn when the app is shipped.

Step 1: define cdn dependencies
Step 2: exclude them from vendor scripts
Step 3: add cdn links to index

[sebastianhenneberg]

The package gulp-cdnizer provides the means to replace paths to local copies of libraries with CDN links. However, the packages works on plain <script> tags. Our tasks are based on loading and concat'ing vendor scripts right from the bower dependencies. We could incorporate a filter and preprocess to achieve the described behaviour.