OpenXML Filter: XLSX: mark columns as metadata

Depends on the resolution of issue #1061 (closed).

The marked metadata columns should be excluded from translation and header values (metadata rows) should be used for context types in context groups:

    <group>
      <context-group>
        <context context-type="Category 1">C1</context>
        <context context-type="Category 2">C2</context>
      </context-group>
      <trans-unit id="tu1" resname="Sheet1!A2">
        <source>Item 1</source>
      </trans-unit>
      <trans-unit id="tu2" resname="Sheet1!B2">
        <source>Item 1 description</source>
      </trans-unit>
    </group>

The following configuration options can be used:

worksheetConfigurations.number.i=1
worksheetConfigurations.0.namePattern=My workheet name
worksheetConfigurations.0.metadataRows=1
worksheetConfigurations.0.metadataColumns=B,C

UI examples:

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