Add isNewScreenshot to Comparison Results

[emilyrohrbough]

Re-logging this issue from zinserjan/wdio-visual-regression-service#83

Often times new screenshots are not generated locally and checked in. This is not caught because our Travis CI builds create new reference screenshots are generated with no indication in the comparison results. It would be helpful to check if for a isNewScreenshot result boolean to assert all screenshots have been properly generated.

The BaseCompare would need changed here

The LocaleCompare would need changes in these places:

1. When new
2. When exists here and here

[emilyrohrbough]

For reference a PR has been submitted to wdio-visual-regression-service by @webOS101 for this feature: zinserjan/wdio-visual-regression-service#103