Add list of comments.

* Added a `LinearLayout` to wrap a variable amount of comments per photo.
* Scrolling slowly down the main `ListView` results in expected behavior, with the user photo, the main photo, followed by three comments.
* Scrolling quickly, however, causes the `ListView` rows to act abnormally.  See gif below.

![hw1_1](https://cloud.githubusercontent.com/assets/588906/4247255/64297cc4-3a57-11e4-8145-c4bf4d89203c.gif)