ADD: Initial COBRA eye tracker interface

The COBRA eye tracker is a custom eye tracker being developed by a
client of iSolver Solutions. It is not available to the general public
(at this time).

This initial commit simply makes the raw eye position data available as
iohub monocular eye sample events. Some initial work on how the client
side calibration will work with the iohub process has also been done.
Merge branch 'master' of git://github.com/psychopy/psychopy
BF: Error in __str__ of iohub KeyboardRelease event

was referencing a non existent class attribute
Merge branch 'master' of git://github.com/psychopy/psychopy
Merge pull request #738 from isolver/master

BF: Error in __str__ of iohub KeyboardRelease event