Add ability to manually adjust cable delays

[jsiegle]

Copying from open-ephys/plugin-GUI#471

Hello,

We have had occasional issues with certain tethers not working correctly due to apparent initialization errors (large amplitude "noise" on some or all channels). Bonsai has a 'CableDelay' setting that can be used to manually set the MISO cable delay value, and that seems to fix our issues. Would it be possible to similarly have user-level access to the cable delay values within the Open Ephys GUI?

Thanks!
Phil