Add a brand new charming installation (for version 0.9) (#144)

* Add a brand new charming installation

* Fix alert position in setup requirements validation

* Add some missing definitions

* A distinction between bootstrap CSS classes and myaac classes

For CSS-styled messages

* Remove unused functions for messages

Co-authored-by: slawkens <slawkens@gmail.com>

system/templates/install.welcome.html.twig

@@ -1,12 +1,17 @@
+<p class="lead">{{ locale.step_welcome_desc }}:</p>
+
 <form action="{{ constant('BASE_URL') }}install/" method="post">
 	<input type="hidden" name="step" id="step" value="license" />
-	<div class="input"><p>{{ locale.step_welcome_desc }}</p>
-		<select name="lang">
+	
+	<div class="input">
+		<select name="lang" class="form-control">
 			{% for locale_ in locales %}
 				<option value="{{ locale_.id }}"{% if (detected_locale is not null and locale_.id == detected_locale) or cookie_locale == locale_.id %} selected{% endif %}>{{ locale_.name }}</option>
 			{% endfor %}
 		</select>
 	</div>
 
+	<div class="text-center m-3">
 	{{ buttons|raw }}
+	</div>
 </form>