QmakeProject: Support absolute path for TARGET

Change-Id: I2b90e0581269b76e27edbe2f28dfda75bb4aa0e5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
QmlLiveTextPreview: Actually use a signal that is fired at text changes

BaseTextEditorWidget::changed only fires for modification state and file
path changes (and will be removed anyhow)

Change-Id: Id1f0ad40adf02ae3949a6ac8500f9de387a9f061
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
TextEditors: Remove unused signal

Change-Id: Iee8d9393b9f203f3a43d7dcc000f4a01d3e3710f
Reviewed-by: Eike Ziller <eike.ziller@digia.com>