Backport fix handling of nested lists
Without this patch, the nesting level can only increase, making the following lists impossible:
1. Elem1
* SubElem1
2. Elem2
* SubElem2
Instead this patch suggest to determine the level of nestidness based on QTextBlockFormat::indent().
See also original pull request to Grantlee: https://github.com/steveire/grantlee/pull/65