Create CSS test class for CDN fallback tests

[Jonas Stjernquist]

Version

version: 2.7.0

Description

I would recommend you to add a test CSS class which easily can be used during CDN fallback tests.

See an example of an CDN fallback test here:
<link rel="stylesheet" href="https://kendo.cdn.telerik.com/2017.3.913/styles/kendo.common-bootstrap.min.css" asp-fallback-href="~/lib_bower/kendo-ui/styles/kendo.common-bootstrap.min.css" asp-fallback-test-class="k-common-test-class" asp-fallback-test-property="opacity" asp-fallback-test-value="0" />

The test CSS class could look like this:
.metisMenu-test-class { opacity:0 }