added control sidebar #10 (#87)

- added configurable sidebar #10
- added language switch in sidebar preferences tab #10
- added sidebar tab with kimai beta-info message #10
- use trait for repositories
- improved README

templates/sidebar/settings.html.twig

@@ -0,0 +1,11 @@
+<h3 class="control-sidebar-heading">{{ 'preferences.title'|trans({}, 'sidebar') }}</h3>
+<div class="form-group">
+    <label class="control-sidebar-subheading">
+        {{ 'preferences.label.language'|trans({}, 'sidebar') }}
+        <select class="pull-right" onchange="window.location.href = this.options[this.selectedIndex].value;">
+            {% for locale in locales() %}
+                <option value="{{ path(app.request.get('_route', 'homepage'), app.request.get('_route_params', [])|merge({ _locale: locale.code })) }}" {% if app.request.locale == locale.code %}selected="selected"{% endif %}>{{ locale.name|capitalize }}</option>
+            {% endfor %}
+        </select>
+    </label>
+</div>