Allow to use analyzer with custom command.

This allows to use scrutinizer without having to install PHPCSFixer, PHP_CodeSniffer, PHPMD,  PHPLOC on the machine, you can use the phars for example.

```yaml
tools:
    php_cs_fixer:
        command: "php php-cs-fixer.phar"
    php_code_sniffer:
        config:
            standard: PSR1
        command: bin/phpcs
    php_mess_detector:
        command: bin/phpmd
    php_analyzer:
        filter:
            excluded_paths: ["*/Tests/*"]
```