[FIX] Livechat not sending desktop notifications

[renatobecker-zz]

Closes #11031.

This PR fixes Livechat desktop notifications that weren't showing up on new messages.

[sampaiodiego]

When enabling Use Real Name I'm getting this notifications:

disclaimer: ao is the livechat visitor's name (the sharp added to it is also weird).. and aue is the message the visitor sent

[sampaiodiego]

I've changed to show a [livechat] in front of the notification title (since we don't a single character to show there - like @ or #):

if visitor has no name, it shows his guest counter:

[rodrigok]

Code approved

[renatobecker-zz]

@sampaiodiego, just give you a feedback on the changes made in this fix..
I really like the approach using roomTypes in cases like this because through this pattern we can keep the code in the correct place, avoiding injecting specific subsystem code into the core notifications system, for example.
So, if we can keep this pattern in the next implementations that are coming, this can make implementation more consistent.

Thanks.