Pass around contents as string, saving repeated
invocation of FormWindowEditor::contents().
Remove dependency to FormWindowEditor.
Reviewed-by: dt <qtc-committer@nokia.com>

 * Ease cross device development by introducing 'targets' which
   group build- and runsettings that are valid for this one target

 Most of the kudos for the code review go to dt. Con, thorbjorn,
 ckandler and others did also review parts of this patch.

Reviewed-by: dt

 * Make sure all non-empty source files found below ./src have
   a copyright header.

Reviewed-by: con

Reviewed-by: Roberto Raggi

Note: I didn't fix all the connects and there are a few missing things.
This compiles, more work is coming.

Also move Designer::Internal::FormWindowEditor ->
Designer::FormWindowEditor.