Added combined X509MixMatchAuthenticator, which allows for logging in both clients with hostname cert and with client name cert

Fixed first client's access without id (IndexError: tuple index out of range) (thanks to Radko Krkos)

getEvents - id<=0 now resets server's notion of client's id to last N events (and starts sending there)

 * Server is now in line with Idea spec concerning client names - they are stored in db and compared lowercase
 * Fixed duplicity check when adding/modifying client
 * Secret is not secret anyway, simplify Client and logging code

* fixed missing 'dml' modifier in some queries

Server now limits max accepted event size. events.data changed to longtext to accomodate longer events

Server now silently logs and skips events which cannot be deserialized from db. That can happen if too big event slips in and db truncates it, causing invalid JSON.

* help message fix