Add ability to paste rich content to the post form

[N3-M3-S1S]

Closes #95

It's also possible to add gifs/images/stickers from keyboards.

[TrixiEther]

@N3-M3-S1S good, have you thought about doing something to notify the user that the sticker or git image is attached? I think a pop-up notification will come in handy here...

[N3-M3-S1S]

@TrixiEther Sure, i will add a toast message.