manifest validator suppresses firing assertions/successful reports

[wschidol]

Some errors in the manifest file are flagged up by the schematron code, but not surfaced to the UI. This is because only failed statements are displayed, not successful statements.

Attached see an MPD in ex62.zip which does trigger the report "@MimeType shall be common between all Representations in an Adaptation Set" but that report is not shown.

The solution is to either also surface successful reports, or to rewrite all reports into asserts. Even though the former would be the smaller change, I tend to the latter which seems cleaner, stylistically. It could also be confusing to the end user to read "successful report" when in fact something is broken in the manifest.