fix(copy): Call split / list modes "Single Panel / Two Panel"

Fixes T5907

CHANGELOG.md

@@ -16,7 +16,7 @@
   + On Windows, the icon is no longer pixelated at many resolutions
   + On Windows, long paths no longer cause installation to fail
   + On Windows, N1 uses the "NylasPro" font correctly
-  + Mark as read now works when viewing messages in split-pane mode
+  + Mark as read now works when viewing messages in two panel mode
   + Basic cut, copy, and paste menus are available for all inputs
   + You can now type in the middle of a search query
   + Names containing "via" are no longer truncated
@@ -34,7 +34,7 @@
   + Hover states in menus and dropdowns are more consistent
 
 - Performance:
-  + In split-pane mode, moving through messages quickly no longer causes jank.
+  + In two panel mode, moving through messages quickly no longer causes jank.
   + Model.fromJSON is 40% faster thanks to optimized loops and other fixes
   + Models are lazily deserialized after being broadcast into other windows
 

docs/InterfaceConcepts.md

@@ -4,7 +4,7 @@ Section: Guides
 Order:   1
 ---
 
-The N1 user interface is conceptually organized into Sheets. Each Sheet represents a window of content. For example, the `Threads` sheet lies at the heart of the application. When the user chooses the "Files" tab, a separate `Files` sheet is displayed in place of `Threads`. When the user clicks a thread in single-pane mode, a `Thread` sheet is pushed on to the workspace and appears after a brief transition.
+The N1 user interface is conceptually organized into Sheets. Each Sheet represents a window of content. For example, the `Threads` sheet lies at the heart of the application. When the user chooses the "Files" tab, a separate `Files` sheet is displayed in place of `Threads`. When the user clicks a thread in single panel mode, a `Thread` sheet is pushed on to the workspace and appears after a brief transition.
 
 <img src="./images/sheets.png">
 

internal_packages/onboarding/lib/initial-preferences-page.cjsx

@@ -16,11 +16,18 @@ class AppearanceModeOption extends React.Component
   render: =>
     classname = "appearance-mode"
     classname += " active" if @props.active
+
+    label = {
+      'list': 'Single Panel'
+      'split': 'Two Panel'
+    }[@props.mode]
+
     <div className={classname} onClick={@props.onClick}>
       <RetinaImg name={"appearance-mode-#{@props.mode}.png"} mode={RetinaImg.Mode.ContentIsMask}/>
-      <div>{@props.mode} View</div>
+      <div>{label}</div>
     </div>
 
+
 class InitialPreferencesOptions extends React.Component
   @propTypes:
     config: React.PropTypes.object
@@ -66,8 +73,8 @@ class InitialPreferencesOptions extends React.Component
     <div style={display:'flex', width:600, marginBottom: 50, marginLeft:150, marginRight: 150, textAlign: 'left'}>
       <div style={flex:1}>
         <p>
-          Do you prefer a single-panel Gmail-style
-          layout or a dual panel layout?
+          Do you prefer a single panel layout (like Gmail)
+          or a two panel layout?
         </p>
         <Flexbox direction="row" style={alignItems: "center"}>
           {['list', 'split'].map (mode) =>

internal_packages/preferences/lib/tabs/workspace-section.cjsx

@@ -79,9 +79,15 @@ class AppearanceModeOption extends React.Component
   render: =>
     classname = "appearance-mode"
     classname += " active" if @props.active
+
+    label = {
+      'list': 'Single Panel'
+      'split': 'Two Panel'
+    }[@props.mode]
+
     <div className={classname} onClick={@props.onClick}>
       <RetinaImg name={"appearance-mode-#{@props.mode}.png"} mode={RetinaImg.Mode.ContentIsMask}/>
-      <div>{@props.mode} View</div>
+      <div>{label}</div>
     </div>
 
 class WorkspaceSection extends React.Component