Revise renderer helper + CSS classes (#580).

BREAKING CHANGES

Webclienr Renderer Helper:
    - dm4c.render.type_icon():
        - the image element rendered is of class "icon" (not "type-icon")
    - dm4c.render.icon(src, title):
        - the image element rendered is of class "icon" (not "type-icon")
        - if "title" is not specified no tooltip will appear (formerly the "src" was shown)

Webclient CSS:
    - class "type-icon" removed.
        It was defined as:
        {{{
        .type-icon {
            border-style: none;
            vertical-align: middle;
        }
        }}}
    - class "menu-icon" removed
        It was defined as:
        {{{
        .menu-icon {
            border-style: none;
            vertical-align: middle;
            padding-right: 12px;
            width: 24px;
        }
        }}}

=> If your plugin relies on these classes it must be adapted.
Basically you might be interested in the reduced icon size (width: 24px).

See #580.