Changes to make query-continue easier

* Add 'continue' to an APIRequest by default
* Move auto-filtering to APIRequest by default
* Move auto_filter to util module
New: util.recursive_merge, util.DynamicList
Make util.recursive_merge copy objects
Prevent sending of duplicate headers (in network.Request)
Implement query-continue

* New method: APIRequest.send_request (moved from APIRequest.request)
* Minor: Added 'import wikibot' to wikibot.api

See #2
Bugfixes

* Disable query_continue in Page.fetch_raw
* Actually disable query_continue in APIRequests (by leaving 'continue' out of request)