Updated StatusBar docs for config.xml preferences.
Updated StatusBar docs for instructions on how to hide it at app startup.
Rewrite file-extras plugin as file-system-roots

This plugin has been updated to work with the new version of File. It
now comes with additional documentation describing the available
filesystem roots, how to use them in applications, and how to configure
them.

The old file-extras plugin still remains, but should be considered
deprecated.