CustomPageXML parsing: allow ":" in value
CustomPageXML parsing: allow ":" in value

In situation where Regions have `:`, this would yield an error, such as the Segmonto syntax:

```xml
<TextRegion id="region_1601885451429_143"  custom="structure {type:NumberingZone:page;}">
```
This fixes this CustomPAGE way to do stuff.
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