[placeholder] add more metadata checks based on EEGNet datasets experience

[christinerogers]

@jeffersoncasimir has some stories to tell... and features to request

[christinerogers]

@jeffersoncasimir can you write some points here -- and also add a point to the WG agenda so that we take a moment to talk about this tomorrow? thanks.
putting this placeholder as Priority:Burning in a new EEGNet ticket also so that we get the notes down asap, tho this task will be done later.

[jeffersoncasimir]

This has been broken down into #126 and #127