Fixed group and child view caching in SimpleExpandableListAdapter.

Now the adapter reports the correct type count and type for group and child
views by overriding the respective methods from the base class. Each group
view has two types, one for expanded views, one for collapsed views. Each
child view has two types, one for the last view within a group, one for the
other views within a group.

Change-Id: I117b2c0f7e98fb7fe2fdd35c15f7d1f9dc06674f
Signed-off-by: Georg Hofmann <georg.hofmann@gmail.com>