Add first autotests for TableView

Testing behavior when using qml and c++ based models. Autotests
based on manual test: tableviewmodels.

Make the tree currentItem available from TableView. Add also
object names for testing purpose.

Including the use of a plugin. The plugin can be used to load other
cpp code needed while testing.

The plugin testplugin will go under qml/QtDesktopTest.

Change-Id: I76e66f35296c6142764bb6027ed9ee49ca50e47b
Reviewed-by: Caroline Chao <caroline.chao@digia.com>