The org.eclipse.ant.ui-implementation (and the underlying
ant-implementation) is able to handle import-tasks (AntImportNode), but
not include-tasks. This patch adds missing node-type (AntIncludeNode)
and "registers" the new node-type at the node-selection-functionality
(AntModel). Furthermore the new node type needs to handle
target-prefixes correctly on included files (according to the
documentation at https://ant.apache.org/manual/Tasks/include.html). This
functionality is also part of this proposed patch and should allow to
use "multi-hierarchical" includes with/without aliases (i.e. "includes
inside includes" with/without using the "as"-property).

Change-Id: I3320c0073c37cdd590d805f2e42f6378fc771100
Signed-off-by: Alexander Blaas <olaf.dev17@gmail.com>