Comment 3 for bug 1188988

Actually, it seems there are facilities in place for that already: https://github.com/PintaProject/Pinta/blob/master/Pinta.Core/Managers/ToolManager.cs#L55

All the tools and brushes are sorted with a comparer function after adding which checks the BaseTool Priority value. When equal, they just get piled in in the order of loading, and right now they're all equal. The default Priority is 75, if we just make the Core Tools have Priority values lower than that they should always be first. (Provided no add-in maker gets cute and gives his/her add-in an even lower number.)