Provide Engine & Log Command Line Arguments

Currently you can override the `config.yaml` location via the command line: ``` ../platypush -c "/path/to/config.yaml" ``` It would be nice if we could override the engine location and log location via the command line like: ``` ../platypush -e /path/to/engine.db -l /path/to/log/dir/ ``` Currently it can be done via the `config.yaml` but it would be nice to do it via the command line. I have Ansible script to deploy the application to my server and `config.yaml` is provided in the playbook before I calculate were the engine or log will be stored. It would be nice to let me set the default locations I expect to deploy the file and if needed I can override it in the `config.yaml` I later deploy.