Composer update - UI enhancements

- Composer height =58px - Frame = 42px
- Replace current scroll to bottom implementation with a scroll to Bottom FAB on both themes
- The text inside the composer frame should be centered
- The padding between the "reveal plus" button, composer frame and Left + Right sides should be at equal distance on default mode
- Verify that the "Send a message..." String matches with the colour indicated on Figma.
- The padding between each component (buttons and composer frame) should be at equal distance on default mode. E.g : It should be at 12px for each gap.
- The input text jumps down when users start typing. It should be centered at all times.
- Remove the Scroll bar in the text frame.
- DARK THEME

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

@@ -19,5 +19,8 @@
   "info" : {
     "author" : "xcode",
     "version" : 1
+  },
+  "properties" : {
+    "template-rendering-intent" : "template"
   }
 }

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

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