Refactor ONIX core interface

[glopesdev]

As discussed in #3 and #4, the current ONIX package depends on design-time hardware connections to the PCIe and other ONI hosts for configuring device properties before and during workflow execution. This can be problematic as it makes it hard to inspect and modify workflows without having an active system plugged in. Having to constantly refresh connections to the host was also found to be problematic on lower-end ONI hosts such as the new USB version of the OE board implementing the ONI standard.

The redesigned interface proposed here assumes a different design stance whereby all device configuration flows from the workflow to the hardware, with no connection required for editing node properties. Initialization is now performed in an explicit chain at the top of the workflow, flowing from the new CreateContext node which is then passed through a series of device initialization nodes before starting acquisition.

ONI device initialization can itself be grouped into "hub" nodes that represent physical assemblies of devices such as the 64-channel or NP headstages. These hubs are now represented and configured explicitly in the workflow. Runtime interactions with devices are still done through sources and sinks for the different device functionalities.

Main features

• No hardware access is required at build-time
• Workflows can be opened and inspected even without physical hardware being connected to the system
• All configuration follows the direction Workflow > Hardware (no state is transmitted from hardware to bonsai)