Let plugins control cursorline

Currently, `cusorline` is forced by  lib/panel 

```
lua/litee/lib/panel/init.lua
472:    vim.api.nvim_win_set_option(win, 'cursorline', true)
```

Consider removing this and letting plugins control this behavior. 

Plugins will control it by performing a `vim.fn.cmd("set cursorline` in their "post_window_create` callback, when registering themselves with the panel.