Display up vs total servers

[aheart]

Add online status boolean to https://github.com/aheart/hearth/blob/master/src/metrics/aggregator.rs#L15
derive(Default) sets booleans to false so it's perfect for us.
On the frontend show {{up}}/{{total}} instead of just total.
Where up is the count of servers with online status boolean set to true.

[Thermatix]

I've created a PR for this -> #74 though I'm not sure how to actually set the online status for the struct on the sever, though I admit I haven't had too much time to go through the code and find it.

[aheart]

@Thermatix, thank you for the PR! I've looked through the code, tested it and left a couple of comments. With several tweaks it should be good to go.

[Thermatix]

@aheart I don't see the comments

[aheart]

Oh, sorry about that. I forgot to submit the review and the comments were only visible for me.

[Thermatix]

@aheart changes made!

[aheart]

Implemented in #74

@Thermatix thank you for your contribution!