Let Twitter-mod retrieve all available tweets in the timeline

* Twitter mod now loads all tweets in your timeline. First run can take a while. Could be improved by batch processing on auto-syncing.
* Changed import() interface to import(bool $forceResync). Forced resyncs are only triggered via the admin interface.
* Twitter mod now only loads tweets that were created since the last sync, unless it's a forced resync.
* Fixed Twitter API to use https connections, as http connections return 403 FORBIDDEN as of tonight. Should have put that in a separate pull-req, just as the style fixes - sorry for the inconvenience.