Heuristics for slot-filling measures & currencies

[gcampax]

If the dialog agent asks for a currency or measure and the user provides a number, we should heuristically convert it. Potentially, this could include a translatable annotation #_[default_unit] associated with the parameter indicating the default unit to use (which would be locale-dependent).

[gcampax]

This issue was transferred from almond-dialog-agent. It should be implemented in terms of templates: we change the templates such that filters and imprecise answers can use numbers where measurements are expected, and generate the right measurement code in the neural network.