Make PaginatedList support the search wrapper JSON

For /search resources the resulting JSON contains 'total_count' and
'items'. The latter is the list PaginatedList expects, so just
transparently use that list. Everything else works just like other
lists.

Also change __grow()'s visibility to allow PaginatedList to use it
in order to peek at 'total_count', making it available as a property.
Add repository search

Qualifiers can be added via keyword args in order to keep the method
uncluttered. Qualifiers could also be given in the query string
directly.
Add user search

Qualifiers can be added via keyword args in order to keep the method
uncluttered. Qualifiers could also be given in the query string
directly.
Add issue search

Qualifiers can be added via keyword args in order to keep the method
uncluttered. Qualifiers could also be given in the query string
directly.