Fix template FileField reading

This merge request fixes all templates where a FileField content was read directly rather than using the associated property who would give the correct output.

Fixes #566 (closed)

beat/web/libraries/templates/libraries/panels/editor.html

@@ -74,7 +74,7 @@
     {% endwith %}
 
     {% if open_source %}
-    <textarea class="form-control" id="code-display">{{ object.source_code_file.read }}</textarea>
+    <textarea class="form-control" id="code-display">{{ object.source_code }}</textarea>
     <p class="help-block">{{ texts.code|safe }}</p>
     {% else %}
     <div class="alert alert-warning">