Fix /contribute link offsets so we can see the headers

[nwinter]

Often we do things like link eager players to specific character classes in the /contribute page, like this: http://codecombat.com/contribute#artisan

When the page loads, though, the scroll doesn't take account the top bar, so we get the character class title cut off:

It should instead scroll like this:

We're already doing something funky with hashes in app/views/kinds/RootView.coffee:

  afterInsert: ->
    # force the browser to scroll to the hash
    # also messes with the browser history, so perhaps come up with a better solution
    super()
    hash = location.hash
    location.hash = ''
    location.hash = hash

    # TODO: automate tabs to put in hashes and navigate to them here

I wonder if this should be fixed on the HTML/CSS side, or if we should just add more code in afterInsert to take the top bar height into account.

[TomSteinbrecher]

I'll investigate making a HTML/CSS fix to this when I look in to the other issue on the contributor page. The better fix for this is most certainly on the HTML/CSS side because applying a fix in script would be more of a bandage than an actual fix.