Add new speakers tag to list all speakers.
Add new speakers tag to list all speakers.

See #507.

artcz/epcon,artcz/epcon,EuroPython/epcon,malemburg/epcon,matrixise/epcon,artcz/epcon,malemburg/epcon,malemburg/epcon,matrixise/epcon,malemburg/epcon,matrixise/epcon,artcz/epcon,EuroPython/epcon,EuroPython/epcon,matrixise/epcon,malemburg/epcon,matrixise/epcon,matrixise/epcon,artcz/epcon,artcz/epcon,EuroPython/epcon,malemburg/epcon