Improve filter context menu

[mikecopperwhite]

Right clicking on a filter with any unconnected pins should offer options to create filters similar to the options available when right clicking on a pin.

These newly created filters will then be auto connected to the right clicked filter because a recent behaviour change to connect newly created filters to the selected filter.

If there's an error connecting them then perhaps the error message should be suppressed since the user may not be expecting this auto connection behaviour.