[ALOY-1729] Add a "widget wide" tss file that serves as the base for the widget (think app.tss for app wide)

When creating a widget it is common to have more than one view, style, controller set. Given the nature of a widget the elements would share a common style. However there is no current way to define a "widget wide" tss file as there is with the "app wide" app.tss file. This means that the author has two choose between two poor coding techniques; - Duplicate the common styles for each tss file within the widget - Pollute the app.tss solely for the benefit of the widget/ This reduces the ability for a widget to fulfil the part of its original goal which was to be DRY and re-usable. The above problem highlights the lack or restrictions of re-usability.