Adds custom titles to various pages in application

Fixes #121 

Logic in `_index.html.erb` feels a little wonky, but seems difficult to test in a helper method. Logic is tested in feature specs.

![screen shot 2014-07-02 at 10 35 15 am](https://cloud.githubusercontent.com/assets/1656824/3459647/4484d9ac-020f-11e4-850a-2f71a193b30f.png)

My comment is just wrt replacing the reference to `title_display` w/ a presenter (which may or may-not ultimately use `title_display` under the hood).