Add "Content declarations"

[msrocka]

This issue tracks the progress for the extension to optionally add content declarations to an EPD data set. A content declaration describes the composition of the EPD's product as a hierarchy of components, materials, and substances. All levels in this hierarchy are optional (e.g. a content declaration could only contain substances).

• Content declarations are written to and read from the data information extension point of an ILCD process data set under the namespace http://www.indata.network/EPD/2019 according to the current ILCD+EPD schema spec., e.g.:

<epd2:contentDeclaration xmlns:epd2="http://www.indata.network/EPD/2019">
  <epd2:component>
    <epd2:name xml:lang="en">wooden panel</epd2:name>
    <epd2:weightPerc epd2:value="100.0"/>
    <epd2:material epd2:recyclable="0.0" epd2:recycled="0.0" epd2:renewable="100.0">
        <epd2:name xml:lang="en">Spruce</epd2:name>
        <epd2:weightPerc epd2:lowerValue="97.0" epd2:upperValue="99.0"/>
        <epd2:mass epd2:value="0.99"/>
        <epd2:substance epd2:CASNumber="123" epd2:packaging="false">
            <epd2:name xml:lang="en">W23</epd2:name>
            <epd2:weightPerc epd2:lowerValue="10.0" epd2:upperValue="60.0"/>
            <epd2:mass epd2:lowerValue="9.0" epd2:upperValue="400.0"/>
        </epd2:substance>
    </epd2:material>
    ...
  </epd2:component>
</epd2:contentDeclaration>

• The content declarations can be viewed and edited in a new tab with two separate trees for non-packaging and packaging materials:

• Items can be added or edited via the context menu (or via a double click
  on the respective item):

• In the upcoming dialog a single item can be edited:

• Depending on the element (component/material/substance) different fields
  are visible: