Migrate my neovim config to home-manager

[yipengsun]

I need to:

• [x] Use Dracula color scheme
• [x] Make sure coc.nvim works
  • [x] Python language server should work
  • [x] ccls MUST work
• [x] Recover my keybindings
• [x] Recover useful macros
• [x] Recover useful plugins
• [x] Integrate editorconfig

[yipengsun]

A few remaining problems:

1. Paste-on-selection is not working
2. Investigate if editorconfig-based right margin highlight is possible
3. Configuration might be needed for texlab.

[yipengsun]

Looks like pynvim solves the first problem.

[yipengsun]

Also need to make sure ~/.tmp/vim is always created.

[yipengsun]

Well, texlab works but is pretty slow.