Support TGS format

[mrozanc]

Implements https://github.com/rainyskye/signal-tgstickers/issues/4

Requires cairo libs for lottie webp support.

[mrozanc]

It looks like the animation is lost using webp, so I'd change the format.

[rainyskye]

I think I had a go at implementing lottie for tgs support, I need to look more into it at some point but have been really busy and haven't felt like/been able to work on it

[mrozanc]

I checked some conversion utils after this attempt and felt like the main issue was the quality of the conversion.

• The resulting APNG have very variable sizes depending both on the animation and its static content.
• The main significant ways of reducing the APNG file size under 300kB are to reduce the frames or the dimensions.
• There should be some limits to set to 1st reduce the number of frames until it's too low, and second if it's still not enough to reduce the dimensions; and it should be applied for each sticker independently to avoid having the lowest quality based on the heavier file in the set.
• The best result I got for the conversion was with this tool: https://github.com/ed-asriyan/lottie-converter