Provide facilitator path option in facilitator init command

[gulshanvasnani]

1. Provide --facilitator-path option in facilitator init command and should write facilitator config to the provided path. If facilitator path is not provided then should write to default path.

2. Currently, the path whether facilitator config is generate is ~/.mosaic/<aux_chain_id>. It should be changed to ~/.mosaic/<origin_chain_id>/<aux_chain_id>/<gateway_address>.json

3. Facilitator start command should load the configs from ~/.mosaic/<origin_chain_id>