[Application] Extract interface

Extract interface from a given class specifier or a glob:

```
$ phpactor class:extract:interface lib/Foobar.php lib/FoobarInterface.php
```

or

```
$ phpactor class:extract:interface lib/Foobar/* lib/Foobar/Api
```

Consider a way to transform names, e.g.:

```bash
$ phpactor class:extract:interface lib/Foobar/* lib/Foobar --transform="/^(.*+).php$/\1Interface.php"
```
