[WIP] Add support for custom emojis

[sonicdoe]

Closes #2. Even though this already works, I’m not sure if I’m happy with some of the internal changes (hence the [WIP]). @EtienneLem Let me know what you think.

An overview of the internal changes I made to support custom emojis:

• The custom category is handled similarly to the recent and search categories.
• The logic for generating the search property is now split out into a separate file so we can use it from both scripts/build-data.js and src/utils.
• <Emoji /> supports custom emojis by checking the emoji.custom property and using emoji.imageUrl to display it (the props themselves remain unchanged).
• Because <Picker /> passes an already sanitized emoji object to <Preview /> it failed for custom emojis. To work around this, I merge the original emoji object (which was passed in via the custom prop) before passing it on to <Preview /> in handleEmojiOver().
• EmojiIndex#search now accepts a custom property which will add those emojis to data.emojis, data.categories, and emojisList so that the rest of EmojiIndex#search works without any changes.
• The anchor icon (an asterisk) is just a quick sketch on my part. If anyone wants to provide a better image, I’d be happy to add it.

Perhaps the custom props could be an object that looks like { name: 'Custom', emojis: [], anchorUrl: '' } so that the anchor can also be customized. I like the idea of customizing the name through I18N, so either works for me.

For the moment, I have opted for I18N. If we allow a custom image for the custom category, I think it would make sense to allow custom images for all categories. I’d therefore suggest a prop akin to backgroundImageFn, maybe anchorImageFn.

[EtienneLem]

Awesome. I’ll take a look either later today or perhaps this weekend.

[sonicdoe]

No worries. I’ll also need to make sure that it works fine with other props such as include, exclude, and emojisToShowFilter. I have only tested the very basic stuff so far.

[EtienneLem]

Welp, I think that’s it! That’s amazing, thank you so much! 🤘

[sonicdoe]

Thank you for implementing the rest of the necessary changes and for releasing v1.0.0 🎉