implement iqdb wrapper

app/logical/iqdb/importer.rb

@@ -0,0 +1,13 @@
+module Iqdb
+  class Importer
+    def import!
+      IO.popen("iqdb add #{Rails.root}/danbooru.db", "w") do |io|
+        Post.find_each do |post|
+          if File.exists?(post.preview_file_path)
+            io.puts "#{post.id.to_s(16)}:#{post.preview_file_path}"
+          end
+        end
+      end
+    end
+  end
+end