EEZ-Flow: Add SCPI processing code generation with UI

[fietser28]

In embedded EEZ-Flow projects I would like to be able to easily generate code that processes SCPI commands. For this a UI interface is needed to specify the SCPI commands (probably a panel derived from existing SCPI panel in studio) and the SCPI errors. In the UI the defined SCPI commands will have some properties, mainly the action (and parameters) the SCPI command will trigger.

Additionally it would be nice if the EEZ-Flow project also generated the definition (IEXT file) to have studio as a control interface via SCPI for the device. During development it would be nice to point to the changing project instead of an IEXT file that needs reloading each time.

SCPI command processing might be done in a different task as the UI processing. I think it would be most flexible to implement a eez_scpi_init() and eez_scpi_tick() functions and give the user freedom to incorporate it in ui_init and ui_tick functions or separately.