storage: allow searching and filtering

[butonic]

This is related to the ListContainerStreamRequest and the Opaque map on the review branch.

For the time being we can implement searching and filtering by using the Opaque property of the ListContainerStreamRequest. In order to collect candidates for new ListContainerStreamRequest properties we should collect the different property keys somewhere.

@moscicki @labkode do you already have keys in mind? I can see

• search with a json encoded pattern, a prefix or a lucene query payload
• pagination with limit and offset or cursor, more details in https://github.com/owncloud/phoenix/issues/116

[butonic]

@labkode I see you closed https://github.com/cs3org/cs3apis/pull/9 Any idea how to tackle this, then?