tmf: Select a target project by default in batch import

tmf: Select a target project by default in batch import

Select the first list item by default in the last page of
the batch import (project selection). On Mac, no item is
selected by default. Since an item is now selected by default,
I changed the behavior of the page's message so that is only
displays an error when nothing is selected. Also, the Eclipse
UI guideline specifies that a page at initialization shouldn't
display an error, see
http://www.eclipse.org/articles/Article-UI-Guidelines/Contents.html#Wizards

Change-Id: I770fb9151f3c74a35dbf2d4e94db08f1301817cb
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/19822
Tested-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
IP-Clean: Matthew Khouzam <matthew.khouzam@ericsson.com>