Correct package loading, uninstallation order

This slightly modifies the order of loading packages in DynamoModel.  It is similar to the fix in the Solar Radiation Analysis library, but it also insures that uninstall is done correct.  In short, this solution insures that package uninstalls are done immediately (i.e. before any other dll's are dynamically loaded) and does package loading last (insuring all requisite libraries are loaded last).  

Note also that NodeModels are loaded last.  This is safe because NodeModels are always dependent on zero touch libraries, never the other way around.  

@ikeough