Add a response to the VERSION command

[dequis]

Numeric 351, followed by 005

This also changes the version string in numeric 004 to be prefixed by "gitter-irc-bridge-" for consistency

Gitter response:

:irc.gitter.im 351 dequis gitter-irc-bridge-1.4.0 irc.gitter.im :
:irc.gitter.im 005 dequis CHANTYPES=# CHANMODES=,,, CHANNELLEN=128 NICKLEN=40 NETWORK=Gitter SAFELIST CASEMAPPING=ascii :are supported by this server

Freenode response, for reference:

:barjavel.freenode.net 351 dx ircd-seven-1.1.4(20170104-717fbca8dbac,charybdis-3.4-dev). barjavel.freenode.net :eHIKMpSZ6 TS6ow 92A
:barjavel.freenode.net 005 dx CHANTYPES=# EXCEPTS INVEX CHANMODES=eIbq,k,flj,CFLMPQScgimnprstz CHANLIMIT=#:120 PREFIX=(ov)@+ MAXLIST=bqeI:100 MODES=4 NETWORK=freenode STATUSMSG=@+ CALLERID=g CASEMAPPING=rfc1459 :are supported by this server
:barjavel.freenode.net 005 dx CHARSET=ascii NICKLEN=16 CHANNELLEN=50 TOPICLEN=390 DEAF=D FNC TARGMAX=NAMES:1,LIST:1,KICK:1,WHOIS:1,PRIVMSG:4,NOTICE:4,ACCEPT:,MONITOR: EXTBAN=$,ajrxz CLIENTVER=3.0 SAFELIST ELIST=CTU WHOX :are supported by this server
:barjavel.freenode.net 005 dx ETRACE CPRIVMSG CNOTICE KNOCK :are supported by this server

Docs: modern, defs, rfc1459 (command), rfc1459 (numeric)