Add commits table and associated columns.
Add migration to remove columns with sha2 hash.
Use the new commit objects.

- Use commit time in the graphs instead of request time.
- Create commit objects on commit hook processing.
Strings not symbols in post commit hook body.
Remove lines from the graphs.
Only show correct runs in the graph.
Merge pull request #32 from TeamAmalgam/better-per-commit

Better handling of commits.