add top padding to 'Show full message...' button

goal is to have roughly the same padding between
message and button as between two paragraphs.
(so that the button look more as belonging to the message
than to the last paragraph)

deltachat-ios/Chat/Views/Cells/BaseMessageCell.swift

@@ -136,6 +136,7 @@ public class BaseMessageCell: UITableViewCell {
         button.addTarget(self, action: #selector(onFullMessageButtonTapped), for: .touchUpInside)
         button.titleLabel?.font = UIFont.preferredFont(for: .body, weight: .regular)
         button.titleLabel?.adjustsFontForContentSizeCategory = true
+        button.contentEdgeInsets = UIEdgeInsets(top: 8, left: 0, bottom: 0, right: 0)
         button.accessibilityLabel = String.localized("show_full_message")
         return button
     }()