Redesign hardware configuration and selection

[bengtmartensson]

Present design is confusing and non-intuitive. Particularly non-intuitive is that the selection of a subpane of Sending HW and Capturing HW selects sending and capturing hardware respectively.

Having "only one instance of each HW class" (prohibiting e.g. sending and capturing with different instances of the same class) is acceptable, due to the nature of the program. (It would not be acceptable in a server-type program, like JGirs.)

Idea: Combine "Sending HW" and "Capturing HW" into one (top-level) pane, "Hardware". The subpanes thereof only opens/closes/configures, they do not select. For selecting there is already Options -> Transmitting hardware and Options -> Capturing hardware, which do the job. They can possibly be doubled by two pull-down combo-boxes under the future Hardware pane.

Related: #246.

Also: allowing the user to select a not-opened device without warning can be confusing.