BF: iohub eye tracker calibration (for tobii and eyelink) keyboard event fix 

Bug caused by Keyboard device event 'key' and 'char' field definition changes.

+ ENH:

- Fixed gcCursor coder demo when used with Tobii.
- Added example of defining use of TheEyeTribe eye tracker in iohub_config.yaml
- Simplified stroop_eyetracker builder demo (removed calculation of average pupil size)