Support pagination of libnpmsearch output

[strogonoff]

We may run into pagination issues now that we cannot do really narrow queries for extensions. We just search for anything mentioning “paneron”, which for now happens to return what we need, and we later filter obtained packages by name & extension metadata anyway.

However, if the “paneron” query starts returning more things and pagination is engaged, we may not obtain all extensions with just one query, so we need to paginate if there’s more than one page of results.

[strogonoff]

Related: #7