Add alternate comparison types to versions

- The types are:
-- Previous: The default and the previously used type
-- Subsequent: Compares against the next version
-- Current: Compares against the current version
- Allow switching between comparison types in index and diff views
-- Have links vary depending upon current comparison type

app/models/note_version.rb

@@ -14,11 +14,25 @@ class NoteVersion < ApplicationRecord
 
   def previous
     @previous ||= begin
-      NoteVersion.where("note_id = ? and updated_at < ?", note_id, updated_at).order("updated_at desc").limit(1).to_a
+      NoteVersion.where("note_id = ? and version < ?", note_id, version).order("updated_at desc").limit(1).to_a
     end
     @previous.first
   end
 
+  def subsequent
+    @subsequent ||= begin
+      NoteVersion.where("note_id = ? and version > ?", note_id, version).order("updated_at asc").limit(1).to_a
+    end
+    @subsequent.first
+  end
+
+  def current
+    @current ||= begin
+      NoteVersion.where("note_id = ?", note_id).order("updated_at desc").limit(1).to_a
+    end
+    @current.first
+  end
+
   def self.status_fields
     {
       body: "Body",
@@ -29,20 +43,32 @@ class NoteVersion < ApplicationRecord
     }
   end
 
-  def was_moved
-    x != previous.x || y != previous.y
+  def was_moved(type)
+    other = self.send(type)
+    x != other.x || y != other.y
   end
 
-  def was_resized
-    width != previous.width || height != previous.height
+  def was_resized(type)
+    other = self.send(type)
+    width != other.width || height != other.height
   end
 
-  def was_deleted
-    !is_active && previous.is_active
+  def was_deleted(type)
+    other = self.send(type)
+    if type == "previous"
+      !is_active && other.is_active
+    else
+      is_active && !other.is_active
+    end
   end
 
-  def was_undeleted
-    is_active && !previous.is_active
+  def was_undeleted(type)
+    other = self.send(type)
+    if type == "previous"
+      is_active && !other.is_active
+    else
+      !is_active && other.is_active
+    end
   end
 
   def self.available_includes