fix discover scss import and improve visualize scss import structure

src/legacy/core_plugins/kibana/public/discover/np_ready/components/_index.scss

@@ -1,2 +1,3 @@
 @import 'fetch_error/index';
 @import 'field_chooser/index';
+@import 'doc_viewer/index';

src/legacy/core_plugins/kibana/public/visualize/_index.scss

@@ -1,10 +1,2 @@
-// Prefix all styles with "vis" to avoid conflicts.
-// Examples
-//   visChart
-//   visChart__legend
-//   visChart__legend--small
-//   visChart__legend-isLoading
-
-@import 'np_ready/editor/index';
-@import 'np_ready/listing/index';
-@import 'np_ready/wizard/index';
+// Visualize plugin styles
+@import 'np_ready/index';

src/legacy/core_plugins/kibana/public/visualize/np_ready/_index.scss

@@ -0,0 +1,10 @@
+// Prefix all styles with "vis" to avoid conflicts.
+// Examples
+//   visChart
+//   visChart__legend
+//   visChart__legend--small
+//   visChart__legend-isLoading
+
+@import 'editor/index';
+@import 'listing/index';
+@import 'wizard/index';