Remove preview from JsonViewer::new, set it elsewhere

This is used in lots of places, so it's not worth changing every single
call to `::new()` just to add `preview`. Just set it right after `::new`
in app.rs and let it default everywhere else.

src/app.rs

@@ -49,7 +49,8 @@ impl App {
             Err(err) => return Err(format!("Unable to parse input: {:?}", err)),
         };
 
-        let mut viewer = JsonViewer::new(flatjson, opt.mode, opt.preview);
+        let mut viewer = JsonViewer::new(flatjson, opt.mode);
+        viewer.preview = opt.preview;
         viewer.scrolloff_setting = opt.scrolloff;
 
         let screen_writer =

src/viewer.rs

@@ -36,7 +36,7 @@ pub struct JsonViewer {
 }
 
 impl JsonViewer {
-    pub fn new(flatjson: FlatJson, mode: Mode, preview: Preview) -> JsonViewer {
+    pub fn new(flatjson: FlatJson, mode: Mode) -> JsonViewer {
         JsonViewer {
             flatjson,
             top_row: 0,
@@ -45,7 +45,7 @@ impl JsonViewer {
             dimensions: TTYDimensions::default(),
             scrolloff_setting: DEFAULT_SCROLLOFF,
             mode,
-            preview,
+            preview: Preview::Full,
         }
     }
 }