Issue title: Drawer cover is not shown
 Issue body: Drawer cover is not shown on Galaxy Nexus(4.2)
```
02-14 13:33:22.202 11551-11551/io.github.droidkaigi.confsched.develop.debug W/OpenGLRenderer: Bitmap too large to be uploaded into a texture (2342x1304, max=2048x2048)
02-14 13:33:22.225 11551-11551/io.github.droidkaigi.confsched.develop.debug W/OpenGLRenderer: Bitmap too large to be uploaded into a texture (2342x1304, max=2048x2048)
02-14 13:33:22.241 11551-11551/io.github.droidkaigi.confsched.develop.debug W/OpenGLRenderer: Bitmap too large to be uploaded into a texture (2342x1304, max=2048x2048)
02-14 13:33:22.256 11551-11551/io.github.droidkaigi.confsched.develop.debug W/OpenGLRenderer: Bitmap too large to be uploaded into a texture (2342x1304, max=2048x2048)
```
![device-2016-02-14-134012](https://cloud.githubusercontent.com/assets/1487505/13031881/91c10086-d320-11e5-86bd-70fba5670c9c.png)
Related with #54 
 Comments: 
 Comment 0: :eyes:  Thanks for your report!!
 Comment 1: First we can try shrink this large image. I didn't do that.
 Comment 2: Close via #232
{'source': 'GithubIssues', 'repo_name_with_owner': 'konifar/droidkaigi2016', 'issue_id': 133505134, 'repo_stars': 732.0}