Improve layout

• Use bootstrap responsive grid for the application lists
• Add a more helpful alt text
• Make the sidebar responsive

Need the following css code in the kde-org in the end of css/applications.css:

#sidebar {
   color: #444;
   min-height: 200px;
   padding-left: 15px;
   padding-right: 15px;
   border: 1px solid #ccc;
   font-size: 10pt;
   text-align: left;
}

@media (min-width: 768px) {
    .order-md-last {
        order: last
    }
    .order-md-first {
        order: first
    }
}

Screenshots: