Make the talk type ordering more explicit.
Make the talk type ordering more explicit.

Also adds support for "interactive" sessions.

PythonSanSebastian/epcon,PythonSanSebastian/epcon,malemburg/epcon,artcz/epcon,artcz/epcon,matrixise/epcon,malemburg/epcon,barrachri/epcon,PythonSanSebastian/epcon,artcz/epcon,artcz/epcon,matrixise/epcon,barrachri/epcon,matrixise/epcon,barrachri/epcon,matrixise/epcon,artcz/epcon,matrixise/epcon,EuroPython/epcon,EuroPython/epcon,PythonSanSebastian/epcon,EuroPython/epcon,PythonSanSebastian/epcon,barrachri/epcon,malemburg/epcon,matrixise/epcon,malemburg/epcon,malemburg/epcon,barrachri/epcon,EuroPython/epcon,malemburg/epcon,barrachri/epcon,artcz/epcon,PythonSanSebastian/epcon