plugins: improve md preview, install ToggleTerm

- Fixes the markdown preview node package installation.
- Removes the markdown preview theme configuration.
- Adds the ToggleTerm plugin that allows to improve the managment of
  terminal buffers and configures it.

Co-Authored-by: iGor milhit <igor.milhit@unige.ch>

lua/custom/plugins/markdownpreview.lua

@@ -1,9 +1,6 @@
 -- makdown-preview.nvim
 -- installed with code found at https://github.com/iamcco/markdown-preview.nvim/issues/558#issuecomment-1514701537
 
--- Force the light theme, no matter the system option is.
-vim.cmd([[ let g:mkdp_theme = 'light' ]])
-
 return {
   {
     "iamcco/markdown-preview.nvim",
@@ -12,6 +9,6 @@ return {
       'markdown'
     },
     lazy = true,
-    build = "cd app && yarn install",
+    build = "cd app && npm install && git reset --hard",
   },
 }

lua/custom/plugins/toggleterm.lua

@@ -0,0 +1,16 @@
+-- A neovim lua plugin to help easily manage multiple terminal windows
+--   https://github.com/akinsho/toggleterm.nvim
+
+-- Set ZSH as shell to get it in a terminal buffer
+vim.opt.shell = "/usr/bin/zsh"
+
+return {
+  {
+    'akinsho/toggleterm.nvim',
+    version = "*",
+    opts = {
+      -- Avoid terminal to be darker than the Nord colorscheme
+      shade_terminals = false
+    }
+  }
+}