Fix crash when adding entry to list below it

The changed signal for the modified nodes was emitted just after the
model was modified, but before Qt had the information that the model
was changing. This was causing it to request data on invalid indexes.

Now the changed signal is emitted after the layoutChanged signal.

Fixes #79
Merge pull request #115 from guillaumecl/fix-move-crash

Fix crash when adding entry to list below it