… node instead Double

Fix the import of some gpx files that uses <Float>instead <Double> node on XProperties

Example
```xml
<Bar id="29">
  <Clef>G2</Clef>
  <Voices>26 -1 -1 -1</Voices>
  <XProperties>
    <XProperty id="1124139520">
      <Float>1.07818</Float>
    </XProperty>
  </XProperties>
</Bar>
```

Adds support for xml Section parsing where sometimes some child tags may not exist, like in this example where only Text child tag is present

```xml
<Section><Text><![CDATA[Pre-Chorus]]></Text></Section>
```