email: add "debug" section to configuration file

email: add "debug" section to configuration file

This patch further extends the configuration file so that it has a debug
section which currently includes replacements for test-mode and preserve
options. These options are very useful for debugging aiaiai, but today
cannot easily be changed without modifying the command line. Instead,
remove them from the options and include them via the configuration
file.

I chose not to add "verbose" to this list, because we actually use
verbose earlier than we parse the configuration. It may still be worth
coming up with some interface where command line options overwrite
configuration options, but I wasn't sure the best way to handle this
yet.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>