Consider extracting Liquid strings from JSON files

[sarahelsaig]

The tool supports extracting strings from Liquid files. But it does not extract Liquid strings from *.recipe.json files. For example the Lombiq Training Demo repo contains a recipe with the "You have no permission to manage Person Page content items." text:

git clone https://github.com/Lombiq/Orchard-Training-Demo-Module.git
cd Orchard-Training-Demo-Module/
extractpo . . -t Liquid
grep "You have no permission" Lombiq.TrainingDemo.pot

It says Lombiq.TrainingDemo: Found 55 strings., but the expected string is not found among them.

[!NOTE] If this is considered dynamic content and intentionally not supported, that's fine too. But in this case a note should be added to the Readme for clarity.