Properly encapsulate internals of the Widget class

[this]

Description: Following internals of the Widget class have been exposed in its sub-classes.

• this.props.glContainer.width
• this.props.glContainer.height
• this.props.glContainer.on(eventName, callback, context)

Also, global.dashboard.registerWidget(widgetName, widgetClass) needs to be encapsulated too.

Affected Product Version: sp-4.1.0