Improve channel notifications

[Alexander Cobleigh]

• we should be able to see that there is a new message in a channel
  (but as a default i think only showing a sigil *default is ideal, rather than a stressful number)
• we should be able to see if we have been mentioned in a channel
  (but as a default only a sigil @default)

[Tod Robbins]

I love/vote for the sigil (* or •) instead of a number and for @default for visualizing a mention. Good ideas, @cblgh!

[Kira Oakley]

a colour could also work, like weechat or irssi

[Alexander Cobleigh]

this is implemented as of #126