Surface, MeshPart: update CurveOnMesh command tooltip and task panel

* Add new icon `MeshPart_CurveOnMesh`, which is the same as
the `Surface_CurveOnMesh` icon but in green color.
The surface icon is used in the Surface Workbench, while the MeshPart
version is currently not used.
* Make the tooltip of the command shorter; the longer instructions
are added in the `TaskCurveOnMesh` task panel.

src/Mod/MeshPart/Gui/Command.cpp

@@ -311,17 +311,11 @@ CmdMeshPartCurveOnMesh::CmdMeshPartCurveOnMesh()
     sAppModule    = "MeshPart";
     sGroup        = QT_TR_NOOP("Mesh");
     sMenuText     = QT_TR_NOOP("Curve on mesh...");
-    sToolTipText  = QT_TR_NOOP("Creates an approximated curve on top of the selected mesh.\n"
-                               "Press 'Start', then pick points on the mesh; "
-                               "when enough points have been set,\n"
-                               "right-click and choose 'Create'.\n"
-                               "\n"
-                               "This command only works with a 'mesh' object, "
-                               "not a regular face or surface.\n"
-                               "To convert an object to a mesh "
-                               "use the tools of the Mesh Workbench.");
+    sToolTipText  = QT_TR_NOOP("Creates an approximated curve on top of a mesh.\n"
+                               "This command only works with a 'mesh' object.");
     sWhatsThis    = "MeshPart_CurveOnMesh";
     sStatusTip    = sToolTipText;
+    sPixmap       = "MeshPart_CurveOnMesh";
 }
 
 void CmdMeshPartCurveOnMesh::activated(int)

src/Mod/MeshPart/Gui/Resources/MeshPart.qrc

@@ -1,8 +1,11 @@
 <RCC>
-    <qresource> 
+    <qresource>
         <file>icons/actions/MeshFace.svg</file>
+        <file>icons/MeshPart_CurveOnMesh.svg</file>
         <file>icons/MeshPart_Create_Flat_Face.svg</file>
         <file>icons/MeshPart_Create_Flat_Mesh.svg</file>
+    </qresource>
+    <qresource>
         <file>translations/MeshPart_af.qm</file>
         <file>translations/MeshPart_de.qm</file>
         <file>translations/MeshPart_fi.qm</file>
@@ -41,4 +44,5 @@
         <file>translations/MeshPart_ar.qm</file>
         <file>translations/MeshPart_vi.qm</file>
     </qresource>
-</RCC> 
+</RCC>
+