Improve feedback regarding album status

Use different icons for errors, complete or partial, modified or not.
Use (unused) info dialog to display error log per album.

![album_modified_2](https://f.cloud.github.com/assets/151042/658338/9fbbd6aa-d5d7-11e2-99e0-f3a18d43f8df.png)
![album_modified_3](https://f.cloud.github.com/assets/151042/658337/9fba11b2-d5d7-11e2-95e6-29be694127bd.png)
![album_modified](https://f.cloud.github.com/assets/151042/658339/9fc0bb20-d5d7-11e2-996f-497bba77f397.png)