Improvement in sessions administration

[davbrican]

-Update of solutions/inputs
-Remove "pairing mode" from GUI (it will be always "MANUAL" in DB)
-Add type of exercise (List of "PAIR" / "INDIVIDUAL") selector
-Remove pairing token (same token 1st option) from GUI ( it will be always "false" in DB)
-By default check "blindparticipant" to true.