load configs from simulator

[Christian-B]

This and related prs cleans up the loading of configs.

config_holder changes

• simplifed untitest config loading to avoid other changes
• standard load conig requires a template is set
• load config not longer creates a template if there is no user config
  • This allows test with a local cfg to work without a user cfg
• new check_user_cfg to be called if machine setup values are all None
  • his then creates the template
  • The exception if a template is created breaks out of the try three times loop
    = All default cfg path are added the same way
• The Main/user cfg files to look for are directly passed into the load_config call

Adds an AbstractSpiNNManSimulation( class with 3 abstract methods

• add_cfg_defaults_and_template
  • will call the local config_setup which finds the default files
  • Sets up the template file (now required)
  • So test and runs have defaults the same
• user_cfg_file
  • Typically the same name as the default at this level but does not need to be
• data_writer_cls
  • As there are now abstract methods no need to pass this all the way down

These allow for the simulator to load the configs and not depend on a previous call.

Spinnman.cfg.template added.