All LDP stream shares standards fields
This commit remove those from the stream mapping and build a request asking only
for the stream specific fields.
`strip_std_field()` will be used to strip fields from the `get_map_props()` in
the next iterations.
This modification aim to format data passed to `strip_std_field()` then
we can use it easyly later for other options.
Previous code was based on demo’s fields to remove undesired one.
As LDP populate hits with some standards fields, this code just remove it.
TODO #13 : build request to retrieve only desired fields
Freezed