Fixed for Roundcube 1.0-RC

1. Fix chbox.php
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<code>
-$rcmail = rcmail::get_instance();
+$rcmail = rcube::get_instance();
</code>
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2. Fix chbox.js
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There's a bug with the list of options in mail page. You need to add a line in 
<skin>/templates/mail.html, if not, when the user saves preferences, the chbox 
column will be hidden.
FIX IT:
<code>
$(document).ready(function(){
    chbox_menu();
var li = '<label><input type="checkbox" name="list_col[]" value="chbox" id="cols_chbox" /><span>'+rcmail.get_label('chbox.chbox')+'</span></label>';
    $("#listmenu fieldset ul input#cols_threads").parent().after(li);
$("#listoptions fieldset:first-child ul.proplist li:first-child").after('<li>'+li+'</li>');});
</code>
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3. add images for skins
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4. Rename skins\default to skins\classic
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5. Add composer.json
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