Make timestamps consistent

[amd-pworfolk]

Per Issue #9, I've reviewed the timestamping behavior. These changes:

1. Use a single build time taken at the launch of the run and now stored as part of the state.
2. Use local time for the build folder name (instead of UTC), making it much easier to find the appropriate build
3. The timestamp field of the stats file still contains the offset to UTC so absolute time can always be determined.

I also added one fix to exit cleanly if the Lemonade cache folder doesn't exist.

Closes #9 .

[ramkrishna2910]

Looks good!