Add themes for 2.x and update installation text

Author: robinheidrich

data/themes.py

@@ -357,6 +357,7 @@
 
 # List of supported phpMyAdmin versions
 PMA_VERSIONS = [
+    '2.6', '2.7', '2.8', '2.9', '2.10', '2.11',
     '3.0', '3.1', '3.2', '3.3', '3.4', '3.5',
     '4.4', '4.5', '4.6', '4.7', '4.8', '4.9',
     '5.0', '5.1', '5.2'

pmaweb/templates/themes.html

@@ -14,9 +14,10 @@ <h2>Themes</h2>
 
 <h3>Installation</h3>
 <p>
-  To install a theme, unzip your downloaded theme into the directory /themes/ of
-  your phpMyAdmin folder. When you open phpMyAdmin, you should be able to select the theme.
-  Please read the documentation for more details.
+  To install a theme, unzip your downloaded theme into the <code>/themes/</code> directory of
+  your phpMyAdmin installation folder. After reloading phpMyAdmin, you should be able to select 
+  the theme from the appearance settings. For more detailed instructions, please refer to 
+  the documentation.
 </p>
 <p>
   You can see the themes in action on our <a href="{% url 'try' %}">demo server</a>.