Add bufferline

[gbaranski]

List of opened buffers on the top, that would help workinng on multiple files at the same time, without using C-o and C-i, or opening file search every time.

Neovim(https://github.com/akinsho/nvim-bufferline.lua)

VSCode:

[kirawi]

Duplicate of #475

[kirawi]

On second thought, this seems more descriptive than the aforementioned issue. Reopening it for now.

[aaron404]

I have an initial implementation here, looking for feedback.
#2759