Merge pull request #263 from blacktaxi/develop

XUnitHelper fails as soon as the test run for any single assembly fails, not running tests for other assemblies.
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Merge pull request #264 from blacktaxi/develop

Added error level setting to XUnitHelper, similar to NUnit error level.
Added ErrorLevel parameter to MSTestHelper config - references #264
#265: moved unit-test related files to the UnitTest folder.