Possibility to change the default configurations for the queue jobs. (#13)

* Add $queue attribute

This code enables me to change the queue name that the JobPipeline will be pushed to.

Now I can do something like this:
```php
JobPipeline::make([
    Jobs\CreateDatabase::class,
    Jobs\MigrateDatabase::class,
    // Jobs\SeedDatabase::class,

    // Your own jobs to prepare the tenant.
    // Provision API keys, create S3 buckets, anything you want!

])->send(function (Events\TenantCreated $event)
{
    return $event->tenant;
})->onQueue('another-queue')
    ->shouldBeQueued()
```

* Add .idea directory to gitignore

* The following methods where added: onConnection, onQueue, delay, tries, shouldBeQueuedOn. The signature of shouldBeQueued was changed too.

* reuse shouldBeQueuedOn

* updating docs

* added timeout

* docs updated

* .phpunit.cache/ added to gitignore

* tests for shouldQueueOn method

* leave only shouldBeQueued method

* update README

* remove unnecessary property declarations

* Delete  jobpipelinetest.json

* add jobpipelinetest.json as a empty file

* update readme

* simplify tests

* improve code

* improve readme

---------

Co-authored-by: Samuel Štancl <samuel@archte.ch>

.gitignore

@@ -2,3 +2,5 @@
 composer.lock
 .phpunit.result.cache
 .php-cs-fixer.cache
+.idea/
+.phpunit.cache/