Set upload dialog background to light.

Fixes #441.
It's possible only certain APIs (<14?) are affected by this. But to be on the safe side, we can simply set it here.

 Alternative is the .xml file, but I wanted to preserve the commented out area in case we want to make it API specific at some point.
Switch code from execution-side to .xml file.

As requested by @cpeterso, background will be set in the ```dialog_upload_observations.xml``` stage.

The progress bar doesn't seem to disappear in Android 2.3 - another bug. Not sure  how to make it work.
Merge pull request #465 from tamcap/bugfix_upload_observations_dialog

Set upload dialog background to "light" (@tamcap)