Fix for: deleting a file leaves garbage at the end of the CloudFileMap.xml file

Anything that caused this file to be shorter than before would render it
unreadable by leaving the end not truncated. The XML Deserializer would
refuse to read these, resulting in having to make a new map, and this
would result in duplicated files.
Get rid of unnecessary StackPanel for Cloud Sync status.
Don't rename SkyDrive files on filename collision.

I'm making the assumption that SkyDrive files are better-managed than
phone isolated storage, which is probably a pretty safe assumption.
Therefore, we shouldn't mess with SkyDrive filenames if we don't have
to. In this case, the single rename is good enough to resolve the
conflict.