trigger: add the name of buffer on trigger monitor when executing a command
trigger: add extra colors in trigger monitor buffer
trigger: add hook command
trigger: add hook focus
trigger: refactor some code in hook callbacks using macros
trigger: parse IRC messages received in signal/modifier hook callbacks

The parsed message is added into hashtable "extra_vars".

For example, signal "freenode,irc_in_PRIVMSG" received with the message
"hello world!" on channel #weechat gives in the hashtable:

  extra_vars:
    tags: ""
    host: "tester!user@host.com"
    tg_signal: "freenode,irc_in_PRIVMSG"
    channel: "#weechat"
    tg_signal_data: ":tester!user@host.com PRIVMSG #weechat :hello world!"
    arguments: "#weechat :hello world!"
    nick: "tester"
    command: "PRIVMSG"
    message_without_tags: ":tester!user@host.com PRIVMSG #weechat :hello world!"