Add unread message count to the room list

[nickvergessen]

Part 1 of #798

[danxuliu]

I think that in this case the counter should be more prominent than the default counter used in other apps so it is easier for the user to see that there are unread messages.

Current:

Proposed (ignore the change in position, it was a quick hack :-) ):

I would also make even more prominent when there is an unread mention (but that would be something for another pull request):

[nickvergessen]

Not our story, the navigation HTML+CSS is managed in the server repo, I'm just copying it to here. We will not change it to be different

[danxuliu]

Yes, I know that the counter style comes from the server. But although consistency with the server is fine, if something does not fit with the needs of an app it should be changed in the app. And the counter of how many unread messages are in a conversation is not the same as, for example, the number of contacts in a group in the Contacts app, and it does not require the same degree of attention from the user either.