Add <title> and <description> for Network Objects

Add <title> and <description> for Network Objects

This patch adds new elements <title> and <description> to the Network XML.
- The <title> attribute holds a short title defined by the user and
  cannot contain newlines.
- The <description> attribute holds any documentation that the user
  wants to store.
- Schema definitions of <title> and <description> have been moved from
  domaincommon.rng to basictypes.rng for use by network and future objects.
- Added Network XML parser logic for the above.

Signed-off-by: K Shiva Kiran <shiva_kr@riseup.net>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>