Message editing (#298)

* Add translation for editing mode

* Add `is_editable` flag to timeline item

* Add edit api implementation

* Add edit context menu action

* Add changelog

* Update Rust package

* Add isEditable into video timeline item

* Fix cyclomatic complexity

* Fix video item thumbnail loading

* Fix not updating timeline layout

ElementX/Sources/Services/Timeline/TimelineItemProxy.swift

@@ -78,6 +78,10 @@ struct EventTimelineItemProxy: CustomDebugStringConvertible {
     var isOwn: Bool {
         item.isOwn()
     }
+
+    var isEditable: Bool {
+        item.isEditable()
+    }
     
     var sender: String {
         item.sender()