Consolidate noise_tests.py into a helper library

[peter-madigan]

Make sure noise_tests are consistently using same buffer clearing / etc

[peter-madigan]

PR #8 moves noise_tests to helpers.noise_tests - a first step
It would be nice to upgrade noise_tests to use the helper functions in helpers.larpix_scripting to address differences in buffer clearing / chip configuration / etc in noise_tests

[peter-madigan]

Keeping open for improvements to noise_tests

[peter-madigan]

PR #11 continues this effort, however I still think there is room for improvement.