Adding Inventory and host Management plus various tidy up commits

[pcuzner]

Multiple changes in this 'bundle', the main features being;

• inventory management: add/remove hosts and groups
• API responses: responses now use a common response object
• Check/create ssh keys on start up
• Add host checks for ssh connectivity, returning our public key if we get "unauthorized" error
• Simplified env/cmdline usage (for tags)

Also addresses the following issues

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