add isHigherBetter flag to the summary report

- Each test should tell if the result is better with higher score or lower score.
- Without this, backend needs to remember which way is better for each test.
- This information should be displayed in visualization / table as well so
  that users do not need to remember which way is better.

Change-Id: I2a54d99e5bc540ee0d0ca4cd1b0ef5f5cb1ebdc5
11 files changed