Add ability for policy to match nodes that have AnyOf or NoneOf the policy tags.

    Adding match_tags field to policies
    
    The match_tags field will allow you to specify the way in which the list
    of tags on a policy will be used.  Available options are 'AllOf',
    'AnyOf' or 'NoneOf'.
    
    For backwards compatibility, the default will be "AllOf" if "match_tags"
    is not supplied during a 'create-policy' operation.  Also in the
    application of the included DB migrate script, any existing policies
    will be set as "AllOf".
    
    There was also a bug in the policy binding SQL code in
    /lib/razor/data/policy.rb that meant that policies with no tags were not
    excluded from matches.

This is in relation to #108 which I know is still up for debate, but it was pretty simple to implement...