Fix for image2 plugin and add missing images (scayt & wsc)

#### iconmaker.js

When I tried to run `iconmaker.js` I had found a problem with two plugins (**scayt** & **wsc**). The script could not update the icons because they didn't exist. Below you can find an error from the console:

```
[i] Checking for changes of (2,3): plugins/wsc/icons/hidpi/spellchecker.png
    [W] Icon plugins/wsc/icons/hidpi/spellchecker.png doesn't exist.
    [+] Icon plugins/wsc/icons/hidpi/spellchecker.png needs update.
        Creating directory plugins/wsc/icons/hidpi

fs.js:642
  return binding.mkdir(pathModule._makeLong(path),
                 ^
Error: ENOENT, no such file or directory 'plugins/wsc/icons/hidpi'
    at Object.fs.mkdirSync (fs.js:642:18)
    at updateIcon (/Users/rb/projects/ckeditor-dev/dev/iconmaker/lib/main.js:112:15)
    at /Users/rb/projects/ckeditor-dev/dev/iconmaker/lib/main.js:94:6
    at compareIcons (/Users/rb/projects/ckeditor-dev/dev/iconmaker/lib/main.js:126:10)
    at /Users/rb/projects/ckeditor-dev/dev/iconmaker/lib/main.js:86:4
    at ChildProcess.exithandler (child_process.js:635:7)
    at ChildProcess.EventEmitter.emit (events.js:98:17)
    at maybeClose (child_process.js:735:16)
    at Socket.<anonymous> (child_process.js:948:11)
    at Socket.EventEmitter.emit (events.js:95:17)
```

Same story for the **scayt**. When I added missing icons, the error disappeared and made the script usable again.

#### build.sh

When I finally managed to regenerate the icons, I ran `build.sh` which merges all the icons into one sprite. Everything was perfect except `image` plugin icon. New version of the icon should be visible but somehow in the sprite I've found the old one. 

After quick investigation, I spotted `image2` directory inside the `plugins` with the standard icon. Updating `location.json` file, solved the problem.

Cheers