iotile registry add_component responding to directory name changes

If you call iotile registry add_component on a folder (e.g. to add virtual device), and path/name to said folder is changed afterwards, IOTile throws an exception.

A warning should be thrown instead of an exception and the folder should be ignored.

Error message : `iotile.core.exceptions.ExternalError: ExternalError: Could not load module_settings.json file, make sure this directory is an IOTile component`

Temporary workaround: go to the virtualenv folder and delete `component_registry.db`