Use _id instead of id everywhere

[patriciagarcia]

When dealing with products we're using product _ids everywhere, which makes it more consistent through the apps. It looks like a good idea to do the same with locations, for example, allow to set the default zone and state by providing the state full _ids (eg. zone:nc:state:kogi) or index byZone and byState using full _ids.

This would need to be adapted in the apps too.