Adding plumbing to detect and display units of measure in a database.
Disabling health information for non-time dbs. All visible formatting
of values goes through wtf.db.Unit.format. Formatting isn't perfect
(we may want to play with different ways of packing the numbers), but it
works.
Work on #299.
Merge pull request #310 from google/units

Adding plumbing to detect and display units of measure in a database.