Fixed link to “home” in some themes

Themes= dark-bar, default, elcaptor, greaves

Link to "Home" non working in case of installation in subdirectory.

Replacing  in `footer.php`:

    <a href="/" title="Return to my website.">Home</a>

by a generated link to site:

    <a href="<?php echo base_url(); ?>" title="Return to my
website.">Home</a>