EnrichedMathMLTransformer should accept any mathml input

[physikerwelt]

• create test case for EnrichedMathMLTransformer with the following input

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block" alttext="a">
  <semantics>
    <mi>a</mi>
    <annotation encoding="application/x-tex">a</annotation>
  </semantics>
</math>

• update endpoint /math/mathoid in vmext-demo and recheck