I added function of soft-delete.

I added function of soft-delete.
So, please consider merging from my repository if possible.

This code support general gems of soft-delete.
- paranoia
- acts_as_paranoid

example
``` ruby
ActiveAdmin.register Nanika do
  actions :all
  soft_delete_actions
end
```
![nanika](https://f.cloud.github.com/assets/4360740/1949471/2143e64a-8109-11e3-8c02-9f479536a10e.png)

added action and batch of soft-delete and restore and hard-delete.

problem
 - I created config/locales/en.yml and ja.yml, because I can't translate locale file without them.

I'm poor at English.
If you can't understand what I mean, please let me know.
Sorry for any inconvinience I may cause you.

I misunderstood.
The action variable of this side is necessary.
The batch_action(L120-123) variable uses this.
``` ruby
 let :batch_action do
+          admin_resource.batch_actions.select{|act| act.sym == action}.first
+        end
```