Move BusinessTemplate_getPythonSourceCodeMessageList to erp5_core, so that coding style tests don't need to install erp5_administration and all its dependencies.

erp5_core is not the final place for this, because this is not required to for business template bootstrap, but this is temporary until we finish business template reorganisation.

This revealed several problems of wrong dependencies between business templates that we could not see before, when coding style was installing too many business templates such as erp5_pdm, erp5_trade, erp5_simulation, erp5_project.