Improve viewer behaviour on errors

[xjiang-at-wiris]

Description

To alllow Viewers to accept multiple MathML inputs and not halt execution of remaining formulas if one MathML format encounters an error.

Steps to reproduce

1. Visit https://htmledit.squarefree.com/
2. Paste the following HTML, which contains a malformed mathml in the third equation:

<script src="https://integrations.wiris.kitchen/KB-43208/html/viewer/node_modules/@wiris/mathtype-viewer/dist/WIRISplugins.js?viewer=image"></script>
<h3>Hi! We're testing the Wiris viewer!</h3>

<p>LaTeX formula:
$$4 - 2 = 2$$
</p>
<p>MathML formula: <math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>x</mi></msqrt></math></p>

<p>MathML formula:
<math>
<mn>2</mn>
<mo>+</mo>
mn>2</mn>
<mo=<s/mo>
<mn>4/mn
</math>
</p>
<p>LaTeX formula:
$$4 - 2 = 2$$
</p>
<p>MathML formula: <math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mi>x</mi></msqrt></math></p>

3. All formula (except the 3rd (problematic)) will be renderer

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#taskid 43208

[carla-at-wiris]

I would mix the last two commits and rebase the code with master, since you have there one duplicated commit from master. Apart from that, the code looks great!