require-api: requireOne, requireOneByXXX, requireByArray

Implementation of #803 

This adds `requireOne()`, `requireOneBy($column, $value)` and `requireOneByArray($values)` to `ModelCriteria`. The `ModelCriteria` also provides magic methods for `requireOneByXXX` and `requireOneByXXXAndXXX`. The generated query classes have `@method`-annotations for these magic methods to support autocompletion. 

---

You can now do something like:

```php
<?php
// ...
try {
  echo 'Hello ' . UserQuery::create()->requireOneById($_GET['id'])->getName();
} catch (\Propel\Runtime\Exception\ModelNotFoundException $e) {
  echo $e->getMessage();
}
```

Which will output 'Hello Marc' or 'User could not be found'  depending on whenever the given user-id exists.

---

You can customize the exception class in the propel config:
```yaml
propel
    generator:
        objectModel:
            notFoundExceptionClass: \Vendor\Project\ResourceNotFoundException
```
or by overwriting the `modelNotFoundExceptionClass` attribute in your query class (or you can overwrite the `createModelNotFoundException` method to customize your exception even more, e.g. when you use a custom constructor signature)


Ah I see :)