Updates based on user feedback

- Checks that the playback volume is not zero.
- Experiments which generate multiple recordings (just GainLinearityExperiment
  currently) now attach their recordings to the results e-mail, just like
  single recording experiments. This adds another four attachments to the
  e-mail, but is required to investigate gain linearity problems.
- Clipping test renamed to Overflow test to conform with Diagnostic Suite
  terminology.
- Updated README with additional supported loudspeaker and better instructions.
- Fixed bug which caused the experiments list to be populated more than once
  under some circumstances.

Change-Id: I6ad05c4657194d04d7d99b9f86ef157942459de4
10 files changed