Fade in/out channels when they're activated/deactivated

[philippitts]

Is your feature request related to a problem? Please describe.

When channels are activated or deactivated, it causes loud spikes in the data.

Describe the solution you'd like

When channels are enabled and/or disabled they should be smoothly transitioned in and out. This could be done by applying a combination of weights and low-pass filters.

[retiutut]

When we change channel settings while streaming data, the ADS1299 is reconfigured and this does caused a small "spike" in the data on most channels. For this reason, the Hardware Settings UI can only be accessed while streaming is off.

Channel On/Off buttons have remained accessible while data is streaming, which is nice for UX and testing, but still can have this unintended effect.

Some early thoughts on this ticket. We could:

• make channel/on off settings only accessible when streaming is off
• do some kind of hardware magic to "hide" the spike, but then results in not accurately depicting what happens on the device