patches/WorkflowTool.py: Workflow Tool migration now happening after install erp5_workflow template.

erp5_workflow: add state_base_category for workflow property sheet, which is necessary for configuration workflow.

erp5_workflow: configuration workflow skin format correction; add variable as allowed content to configuration workflow; correct skin listbox selection field.

ERP5Site.py: the Workflow Tool installation has been move to the bootstrap to allow migrating automatically.

ERP5WorkflowTool.py: add bootstrap function to migrate the workflow tool conditionally-autoomatically.