base, js (websocket), css (main style): dynamic pages implementation, first draft: this patch introduces the browser part of dynamic pages. Dynamic pages work by establishing a websocket between server and the current page, if requested by server (which means that needed arguments are present in template). Once the connection is established, the server can, for now, reload the page, append HTML elements, or receive arbitrary data (without reloading the page, in opposition to data post). If connection can't be established, a popup will be displayed and connection will be retried many times after variable timeouts. The browser will finally give up and display an alert to client if the number of retries is too high (20 for now).

#body {
    display: flex;
    flex-direction: column;
}

.invitation_header {
    flex: 1
}

.invitation_header h1,p {
    text-align: center;
}

#include_main {
    flex: 9
}

#include_main {
    width: 100%;
    margin: 0;
    border: none;
}

footer {
    /* footer should already be displayed in included page */
    display: none;
}