Clean up g_ana angle implementation.

Clean up g_ana angle implementation.

- Remove -split1 and -split2 options, as the 'merge' selection keyword
  can be used for the same effect.
- Remove -multi option, as the same can be interpreted from the number
  of input selections (not currently supported, though).
- Change output options, such that averages and individual angles are
  written to different files, allowing the removal of -all option.
- Add tests.
- Add some TODO comments for things still missing.

Supporting changes:
- Add an analysis data module that computes per-frame averages and tests
  for the module.
- Also add tests with multipoint data for the average modules and fix an
  issue in mock_datamodule.cpp (now this is somewhat unrelated, but some
  intermediate version of this change was more tightly coupled to
  multipoint data).

Change-Id: I0c62c2c54a0b3a0ff269ea0c2d6150c31479f3eb