use team as entry in Maintainer field of debian/control

As discussed today we shouldn't use a specific Maintainer in
debian/control field but instead just use a team entry since
there might be multiple persons involved per package and
iff we want to track this kind of information outside of
svn [log|blame|,...] we shouldn't make that visible to the
outside per se

From: Michael Prokop <mprokop@sipwise.com>

debian/control

@@ -1,7 +1,7 @@
 Source: ngcp-metapackages
 Section: utils
 Priority: extra
-Maintainer: Jon Bonilla <jbonilla@sipwise.com>
+Maintainer: Sipwise Development Team <support@sipwise.com>
 Build-Depends: debhelper (>= 5)
 Standards-Version: 3.9.2
 Homepage: http://sipwise.com/