Many Pages now show ELO

* Elo added to match request page
* Elo added to match page
* Elo added to user show page
* Elo added to dashboard
* Elo added to user index page
* Dashboard shows last 5 matches
How can we make this more semantic? Array access is vague. It would be nice to see something like

```
match.defender.update(elo: new_elos.defender_elo)
match.challenger.update(elo: new_elos.challenger_elo)
```
Or something along those lines that would be more clear than a (seemingly) arbitrary array access.