[Feature request] Autoselect report on devices where there is only one reportable media

[GoogleCodeExporter]

- What steps will reproduce the problem?
1. Install on Nexus 4 or 7 (or probably any Android device without SDCard)
2. Launch application
3. DiskUsage ask from what storage it must report usage, but there is only one

- What is the expected output? What do you see instead?
It would be nice to go directly to the report, without having to choose between 
one choice.

- What version of the product are you using? On what operating system?
Current version (3.4) of app on current version of JellyBean (4.2.2)

The application is already great and really useful in present state. It could 
go to five stars and a half ;-) with this feature.

Original issue reported on code.google.com by lfourrier on 22 Feb 2013 at 3:59