Make hardware sets configurable via dialog

[alexdewar]

It would be useful to let users define their own hardware sets (possibly basing them on the default FINESSE/UNIRAS configuration settings). The problem with only providing built-in configurations is that if a single property changes (e.g. the user changes the type of temperature monitor used in the rig or wants to modify a device parameter), it will not be able to incorporate these changes into a hardware set without modifying FINESSE's source code.

Some of this code can likely be cannibalised from the existing DeviceControl implementation.

[alexdewar]

NB: This task will probably take a while.