Add support for custom Emoji packs

[Barina]

In continuation of issue #14
Add the ability to change the Emoji's to a custom pack.

Before delving into this, we need to acknowledge that Telegram is currently working on a new shiny Telegram web and everything we did will have to change.
This will also applied here and we also don't really know about their progress and don't have a release date.. I can't find any info on this anymore, but the only thing I know that it is in pretty good shape so it can be released very soon.
That's why I don't really wanna get into big changes here now and wait for the big changes in the new Telegram website.

This needs further investigation as well, as of now it seems that Telegram uses 5 sprite sheets for emojis (links below) and their CSS takes a portion of it for each emoji.

So we have several options here.. We can

• Find similar sprite sheet with different icons that'll fit in the correct order. also the size of the sheet and the icons is important.
• Generate new icons by either drawing them ourselves or using 3rd party free to use pack. like the twitter one. this is time consuming specially the "drawing ourselves" part 😅
• Drop the sprite sheet approach and use individual icons like I did with most of the icons in this style.. I drew them myself (kinda copy them actually) to an SVG so they'll look nice in any scale. but this is way more work and not recommended at all as I'm not that talented unfortunately..

If we do make our own files we'll need to store them either on the Github project or embed them in the style file if possible.
The later is less recommended in my opinion as it will result in huge file unlike the first approach where we can keep them as simple links.

Sprite sheets:
https://web.telegram.org/img/emojisprite_0.png
https://web.telegram.org/img/emojisprite_1.png
https://web.telegram.org/img/emojisprite_2.png
https://web.telegram.org/img/emojisprite_3.png
https://web.telegram.org/img/emojisprite_4.png

[Barina]

@Cyberdroid1 you mentioned EmojiOne font as emoji pack in issue #14
I just realized it is called "Twitter Color Emoji SVGinOT Font" now and it's what I refer to above.
Here the liscense is CC-BY-4.0 which only requires attribution in the project readme file or anywhere in our "product" so we can use it.
And is also have SVG version which is good.. but individual files which is lots of work 😅

[prakharb5]

Oh, if it is a lot of work, no need of it then. The current ones are just fine.

Even I had noticed that the Telegram Web version is currently 0.7, meaning that a proper v1 release is pending.

If you have time, you can do it, but I don't think it would be worth the time and effort, given the new web version is near.

[Barina]

I saw a video about it like 6 months or more.. I can't find any info about it anywhere.
Luckily this project is open for pull requests so anyone can contribute ;)