Rename INSTALL_DEFAULT_UNATTEND to IGNORE_UNATTEND

 * Rename the image property INSTALL_DEFAULT_UNATTEND to
   IGNORE_UNATTEND.
 * Add documentation about this property
Rephrase a comment in the defaults config file
docs: Update the copyright to include year 2014
docs: Add a Windows deployment section

This contains basic info on how the Windows images get deployed and
instruction on how to use a custom Unattend.xml file.
windows: Consider Autounattend.xml as answer file

When searching a windows image for the presence of an answer file,
make sure that Autounattend.xml is also considered as answer files.