Remove token after used or when expired

This commit will close issue #96 

1) Remove token after first use
2) Remove token not used after first use > 24h
3) Semi rollback of previous commit: we must check matricola and token when signup/reset so they have to be in knownKeys. Instead the removal of hash was correct
4) Some mini debug text improvement

Tested on live Highgarden

writeStudentInfo() in '/registry/backend.js' from 'line 211' to 'line 218': if there isn't 'matricola' in 'knownKeys' it doesn't complete its workflow.