create a simpler method of handling the BC ModUrl issue

A simpler method of dealing with this issue. I think this is all the changes that would need to be made. All BC would continue to work and new modules could simply use the Route based side of ModUrl

```php
        $aUrl = new ModUrl();
        $aUrl->setRoute('zikuladizkusmodule_user_viewforum', array('forum' => 2));
        $bUrl = new ModUrl($this->name, 'user', 'viewforum', null, array('forum' => 2));
        $a = $aUrl->getUrl();
        $b = $bUrl->getUrl();
        var_dump($a, $b);
```
outputs:
> string(28) "/core.git/src/forums/forum/2" string(28) "/core.git/src/forums/forum/2"

ping @cmfcmf @Guite @drak 

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| Refs tickets  | #1945, #1940, #1937, #1947
| License       | MIT
| Doc PR        | -
with your other suggestion, `$this->language` could be null also?