Retrying & deleting failed messages

- Display an exclamation mark (on a red background). In case of a multi-line message
- When a message with an error is selected, show a bottom bar with the 4 following actions: Retry - Delete - Edit - Copy
- If users press on Delete, a confirmation dialog is displayed
- When error messages occur, a general error message appears above the composer. Selecting Delete will delete all error messages. Pressing on Retry will attempt to resend error messages
- If users press on Delete, a confirmation dialog is displayed
- In room lists, decorate rooms with errored messages with the error icon. Rooms with errors should be sorted first

Riot/Assets/Images.xcassets/Common/error_icon.imageset/Contents.json

@@ -0,0 +1,23 @@
+{
+  "images" : [
+    {
+      "filename" : "error_icon.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "error_icon@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "error_icon@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}