remove getAllUpdates() and add a typical replicatio API for the update call (#3081)

* (r10s, adb, hpk) remove getAllUpdates() and add a typical replica-API that works with increasing serials.  Streamline docs a bit.

* adapt ffi to new api

* documentation: updates serials may have gaps

* get_webxdc_status_updates() return updates larger than a given serial

* remove status_update_id from status-update-event; it is not needed (ui should update from the last known serial) and easily gets confused with last_serial

* unify wording to 'StatusUpdateSerial'

* remove legacy payload format, all known webxdc should be adapted

* add serial and max_serial to status updates

* avoid races when getting max_serial by avoiding two SQL calls

* update changelog

Co-authored-by: B. Petersen <r10s@b44t.com>

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### API changes
+- change semantics of `dc_get_webxdc_status_updates()` second parameter
+  and remove update-id from `DC_EVENT_WEBXDC_STATUS_UPDATE` #3081
+
 ### Changes
 - add more SMTP logging #3093
 - place common headers like `From:` before the large `Autocrypt:` header #3079