Add user config to enable line wrapping in the staging view

It is enabled by default, because I think it's often helpful, and rarely in the
way. I bet most user won't even notice.

schema/config.json

@@ -96,6 +96,11 @@
           "description": "How the window is split when in half screen mode (i.e. after hitting '+' once).\nPossible values:\n- 'left': split the window horizontally (side panel on the left, main view on the right)\n- 'top': split the window vertically (side panel on top, main view below)",
           "default": "left"
         },
+        "wrapLinesInStagingView": {
+          "type": "boolean",
+          "description": "If true, wrap lines in the staging view to the width of the view. This\nmakes it much easier to work with diffs that have long lines, e.g.\nparagraphs of markdown text.",
+          "default": true
+        },
         "language": {
           "type": "string",
           "enum": [