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/Modules/Room/Views/Activities/RoomActivitiesView.h

@@ -73,16 +73,6 @@
  */
 - (void)displayOngoingConferenceCall:(void (^)(BOOL video))ongoingConferenceCallPressed onClosePressed:(void (^)(void))ongoingConferenceCallClosePressed;
 
-/**
- Display a "scroll to bottom" icon.
- Replace the current notification if any.
- 
- @param newMessagesCount the count of the unread messages.
- @param onIconTapGesture block called when user taps on notification icon.
- */
-- (void)displayScrollToBottomIcon:(NSUInteger)newMessagesCount onIconTapGesture:(void (^)(void))onIconTapGesture;
-
-
 /**
  Notify that the a room is obsolete and a replacement room is available.