[Finder] Shell escape and windows support

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Add escaping of command passed to Shell::testCommand().
Fix todo add support for windows.
a "better way" if `command` is not available - maybe even prefered over using `command` - is `which`

```
$ command -v ls
alias ls='ls --color=auto'

$ which ls
/bin/ls
```