Creates the dialog box to select which sites to import from the file
selected in mainwindow.cpp. The DivesiteImportModel is created as a
table to display and select which sites are to be imported. Once the
sites are selected, the Command::importDiveSites command is called to
add the sites to the core dive site table with undo/redo functions.
Signed-off-by: Doug Junkins <junkins@foghead.com>
