[TD]Fix section snapping (fix #15961) (#15450)

* [TD]Add view snapping preferences

* [TD]fix section snapping algo

- snap sections to section normal line.
- snap views to other views in X&Y

* [TD]fix snapping to ProjectionGroups

src/Mod/TechDraw/Gui/DlgPrefsTechDrawGeneralImp.cpp

@@ -79,6 +79,8 @@ void DlgPrefsTechDrawGeneralImp::saveSettings()
 
     ui->cb_useCameraDirection->onSave();
     ui->cb_alwaysShowLabel->onSave();
+    ui->cb_SnapViews->onSave();
+    ui->psb_SnapFactor->onSave();
 }
 
 void DlgPrefsTechDrawGeneralImp::loadSettings()
@@ -124,6 +126,9 @@ void DlgPrefsTechDrawGeneralImp::loadSettings()
 
     ui->cb_useCameraDirection->onRestore();
     ui->cb_alwaysShowLabel->onRestore();
+
+    ui->cb_SnapViews->onRestore();
+    ui->psb_SnapFactor->onRestore();
 }
 
 /**