feat: add toggleterm, markdown preview keymaps, lualine switch filename and navic (#23)

- Configured toggleterm plugin
- Added keymap for markdown preview
- Changed lualine so Navic is better readable by switching filename and
type with Navic.

config/plugins/utils/markdown-preview.nix

@@ -15,4 +15,15 @@ _: {
       };
     };
   };
+
+  keymaps = [
+    {
+      mode = "n";
+      key = "<leader>mp";
+      action = "<cmd>MarkdownPreview<cr>";
+      options = {
+        desc = "Toggle Markdown Preview";
+      };
+    }
+  ];
 }