Replace Firefox OS emoji font

replace emoji

first backup you profile!!!
use [https://github.com/Mozilla-TWQA/B2G-flash-tool/blob/master/backup_restore_profile.sh] to do so.

then, create a backup of the default emoji font

```shell
adb pull /system/fonts/NotoColorEmoji.ttf
```

then rename your emoji font to NotoColorEmoji.ttf for convenience and run:

```shell
adb remount
adb shell stop b2g
adb push NotoColorEmoji.ttf /system/fonts/
adb shell start b2g
```

Gaia should restart and you'll be able to see the new set of emojis