widget plugin structure

[sorin-costea]

Adding a widget plugin structure will enable new widgets to be designed in separate JavaScript files.

An example might be a new Grid Widget. A Javascript file called "grid_widget.js" could be developed. It will then be possible for the main API "mm.js" to pick up this new widget so that it can be added to Swanc with no code changes to "mm.js".

Having a widget plugin structure will enable other developers to quickly develop new widgets that can be shared.