Break analysis into phases

[mscottford]

To assist with user communication, I think we need to break the analysis into separate stages. Each of these stages would probably have a corresponding status value for status reporting. I think it would also be useful to start collecting performance metrics around how long each of these steps takes

• Cloning repository
• Detecting manifests
• Scanning repository history
• Looking up dependency versions and dates - happens for each manifest (once we add support for more than one at a time per Handle multiple manifests design #10)
• Computing metrics - happens for each metric and for each manifest (once we add support for more than one metric)