Closure Compiler

Missing options
setLanguage, setFormatting, setWarningLevel

* Allows the usage of --language_in (Compiles AngularJs 1.x and Ember.js with ECMASCRIPT5)
* Allows the usage of --formatting (PRETTY_PRINT etc.)
* Allows the usage of --warning_level (DEFAULT, VERBOSE, QUIET)
feature #260 Closure Compiler (peshi)

This PR was merged into the 2.4-dev branch.

Discussion
----------

Closure Compiler

Missing options
setLanguage, setFormatting, setWarningLevel

* Allows the usage of --language_in (Compiles AngularJs 1.x and Ember.js with ECMASCRIPT5)
* Allows the usage of --formatting (PRETTY_PRINT etc.)
* Allows the usage of --warning_level (DEFAULT, VERBOSE, QUIET)

Example usage (tested with latest stable ember.js and handlebars.js and Twitter Bootstrap 3.0.x):
```
assetic:
 ...
    filters:
        closure:
            jar: /usr/local/bin/compiler.jar
            compilation_level: SIMPLE_OPTIMIZATIONS
            formatting: PRETTY_PRINT
            language: ECMASCRIPT5
            #warning_level: DEFAULT
            apply_to: "\.js$"
```

```
            {% javascripts filter='?closure' output='js/compiled-ember.js'
            '@YourBundle/Resources/public/js/handlebars-v1.2.0.js'
            '@YourBundle/Resources/public/js/ember.js'
            '@YourBundle/Resources/public/js/ember-data.js'

            %}
            <script type="application/javascript" src="{{ asset_url }}"></script>
            {% endjavascripts %}
```

Commits
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60ef010 Closure Compiler