For #1907: output row/col information
For #1907: output row/col information

- side-effect: fr:grid supports nested xf:var/xf:group in editable/repeat cases
- refactor fr:grid a bit

joansmith/orbeon-forms,ajw625/orbeon-forms,tanbo800/orbeon-forms,martinluther/orbeon-forms,brunobuzzi/orbeon-forms,orbeon/orbeon-forms,ajw625/orbeon-forms,martinluther/orbeon-forms,brunobuzzi/orbeon-forms,wesley1001/orbeon-forms,orbeon/orbeon-forms,joansmith/orbeon-forms,joansmith/orbeon-forms,ajw625/orbeon-forms,tanbo800/orbeon-forms,orbeon/orbeon-forms,martinluther/orbeon-forms,tanbo800/orbeon-forms,ajw625/orbeon-forms,martinluther/orbeon-forms,wesley1001/orbeon-forms,joansmith/orbeon-forms,orbeon/orbeon-forms,wesley1001/orbeon-forms,brunobuzzi/orbeon-forms,tanbo800/orbeon-forms,brunobuzzi/orbeon-forms,wesley1001/orbeon-forms