Update getting pushrules, add tests, tweak pushrules (#2705)

This PR
- adds tests for `evaluatePushrules`
- removes the need for the UserAPI on the `OutputStreamEventConsumer`
(for easier testing)
- adds a method to get the pushrules from the database
- adds a new default pushrule for `m.reaction` events (and some other
tweaks)

internal/pushrules/util.go

@@ -11,7 +11,7 @@ import (
 // kind and a tweaks map. Returns a nil map if it would have been
 // empty.
 func ActionsToTweaks(as []*Action) (ActionKind, map[string]interface{}, error) {
-	var kind ActionKind
+	kind := UnknownAction
 	tweaks := map[string]interface{}{}
 
 	for _, a := range as {