[bugfix/chore] Refactor timeline code (#1656)

* start poking timelines

* OK yes we're refactoring, but it's nothing like the last time so don't worry

* more fiddling

* update tests, simplify Get

* thanks linter, you're the best, mwah mwah kisses

* do a bit more tidying up

* start buggering about with the prepare function

* fix little oopsie

* start merging lists into 1

* ik heb een heel zwaar leven
nee nee echt waar

* hey it works we did it reddit

* regenerate swagger docs

* tidy up a wee bit

* adjust paging

* fix little error, remove unused functions

internal/timeline/timeline_test.go

@@ -34,8 +34,10 @@ type TimelineStandardTestSuite struct {
 	tc     typeutils.TypeConverter
 	filter *visibility.Filter
 
-	testAccounts map[string]*gtsmodel.Account
-	testStatuses map[string]*gtsmodel.Status
+	testAccounts    map[string]*gtsmodel.Account
+	testStatuses    map[string]*gtsmodel.Status
+	highestStatusID string
+	lowestStatusID  string
 
 	timeline timeline.Timeline
 	manager  timeline.Manager