Fixing OS specific issues with logging

[davidorme]

This PR removes some code from the logger counter handler reset method to fix #113.

It also:

• Updates the _safedata_validate_cli entry point to allow the log and JSON outputs to take optional paths, partly to make it easier to test, partly to take away fixed paths.
• Uses that entry point with existing test fixture files to perform an actual test of the safedata_validate entry point.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (177abd5) 78.11% compared to head (4f05e97) 79.37%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #114 +/- ## =========================================== + Coverage 78.11% 79.37% +1.26% =========================================== Files 13 13 Lines 3674 3671 -3 =========================================== + Hits 2870 2914 +44 + Misses 804 757 -47 ```

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