Composer update - UI enhancements

- composer max height
- unread messages on scroll to bottom button
- changed input toolbar background
- new missed discussions notifications
- Edit a message mode
- Reply to a message mode
- support for landscape mode

Riot/Assets/Images.xcassets/Room/Input/input_close_icon.imageset/Contents.json

@@ -0,0 +1,26 @@
+{
+  "images" : [
+    {
+      "filename" : "input_close_icon.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "input_close_icon@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "input_close_icon@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  },
+  "properties" : {
+    "template-rendering-intent" : "template"
+  }
+}