improvement: bug fixes and refactors

- power level content override adds to the default event instead of
replacing it
- sending code refactored to make edus possible
- remove presence events when restarting conduit
- remove room_id field from read receipts over /sync
- handle incoming read receipts
- fix array bounds bug in server_server.rs

Cargo.toml

@@ -106,3 +106,7 @@ conf-files = [
 ]
 maintainer-scripts = "debian/"
 systemd-units = { unit-name = "matrix-conduit" }
+
+# For flamegraphs:
+#[profile.release]
+#debug = true