Update emojis
This PR adds scripts to parse NotoColorEmoji.ttf (https://github.com/googlei18n/noto-emoji doesn't include flags) and extract emojis, to remove useless margins and to generate sprites from emoji-categories.xml (can be found in Android source code).
And it updates emojis in Silence with newly extracted ones.
Emoji flags are disabled for now because they are not parsed properly.
Fixes #384 (closed).