Replaced default sticker set with twitter emoji

[fpohtmeh-github]

Twitter emoji set is a very popular sticker set. Looks much better than current one

[DamirPorobic]

Thanks for taking your time and providing this PR. I don't know if you knew this but you can upload your own stickers and hide the default ones, which I personally actually like, that's why I added them in the first place. Adding twitter emojis kind of creates an affiliation with a big software corporation. And last, what's the licence on the twitter emojis?

[fpohtmeh-github]

Twitter emoji graphics have license CC BY 4.0. I'll add license into stickers folder if we leave them.
Default sticker set if the first impression of anyone who installs KSnip. Only 5% (even less) will play with custom sticker sets. That's why important to have well-looking defaults in application. Twitter set is popular, attractive and well-known.

I don't want to insult developers of current sticker set, but it looks too simple for serious software. Such graphics style was popular 20 years ago. Old school is not for everyone, but KSnip is :)

[fpohtmeh-github]

I can look for another emoji set, but strongly recommend don't leave current one because it's not for masses.

[DamirPorobic]

I can look for another emoji set, but strongly recommend don't leave current one because it's not for masses.

Thanks. We can change it but I'm kind of not warm with this one. Just link me any other example you find before you go through adding them again.