Add Mirage Cask

This PR adds a cask for Mirage 1.0.1.

The `url` and `homepage` fields point to Softpedia as the [original developer's website](http://www.itaiferber.com) is no longer available.

The description of the application on Softpedia's website reads:

```markdown
Mirage is a free Cocoa based application which will make your dock,
separator, indicator and even Stacks totally clear.

Mirage will allow you to:

- Install a clear dock.
- Install a clear separator.
- Install clear indicators.
- Install clear stacks.
- Restore any combination of those straight from default.
```