Use `x` as argument of all the functions accepting a datapackage

[damianooldoni]

At the moment package is used. Replace it with x everywhere. Similar behavior in camtrapdp. We do it already in the reexported function read_camtrapdp(). It's a breaking change of course, but this is the less dangerous probably as the first argument is rarely called with its name like f(package = ).

[damianooldoni]

Close as completed via #325