Stop dynamically including CSS files in tests #393

Dynamically loading CSS files is an asynchronous process and our
heuristics for detecting when CSS files are done loading don't appear to
be working consistently on Saucelabs. Make our tests more robust by
statically loading CSS files instead.

This change removes the tests in styles-uidark/light.js These tests would
have needed quite a bit of changing to remove the dynamic CSS dependency
and they do not provide very much coverage. We will add a more
comprehensive set of styles tests in the future.

Also updated CorsicaTests.Utilities.testMetrics.

This change removes all test helpers for dynamically loading CSS files
because they weren't robust. There are no remaining tests which
dynamically load CSS files.
"Namespace" rules in Metrics.less #393

Prefix every rule in Metrics.less with a special class so that its rules
are only in effect for the tests that need the rules.