#634 User-extensible widget bar

[Steve Keen]

This is a proposal to support adding vertical markets to Ravel, by enabling users (more realistically, us) to create widget toolbars that support specific industries--like actuaries for example.

As with tabs at present, the widget bar would end with a + key which enables a new widget menu to be added. The user would name the bar--we may have to restrict this to TLAs initially--and then be able to add widgets to it.

The ideal way to do this would be to enable drag and drop from the canvas onto the new widget, but as an interim we could allow choice to be made from a (veyr big!) form that included all current mathematical operators.