ajaxbased resync

i implemented a resync which is controlled by the browser. foursquare
uses a limit/offset-based pagination, for instagram i implemented the
next_url - based pagination, it shoud be easy to adopt for other mods i
recently not use. currently i copied the import-functions in the
foursquare and instagram - mod to support the ajax-requests. they should
be next combined with the import()-methods to support pagination-based
imports. this functionality is dependend on what the count_items -
method counts, because the import stops, when this number is reached.
for me it works with instagram and foursquare because from all their
items are posts created. when there is a filtering during the map_data -
process, count_items must filter these items out. instagram-favs are not
imported by this process, because it is restricted to one item-set.
maybe that they can be imported by a second ajax-method.