Nicer keypad layout for calls dialer
The keypad in Calls currently has a few layout issues, including
+is on the wrong key (Should be below the 0 rather than the *)
#keys should be vertically centered
#keys should be SVG icons instead of characters
Since we'll change HdyDialer anyway to make it more appropriate for the various specific use cases, this would be good to keep in mind for the variant we'd use in Calls (#7).
For reference, this is what it looks like on iOS and Android: