Implements #6582 Autoresponder in HTML format

Changes to implement autoresponder mail in html format.

To complete this feature there are 2 missing changes:

1. extend the dbispconfig database structure in order to save the status of HTML switch. I've done that manually via commands like: USE dbispconfig; ALTER TABLE mail_user ADD autoresponder_html enum('n','y') NOT NULL DEFAULT 'n'; (I don't know how to save this change in ISPConfig3 project)

2. modify the roundcube plugin to implement the main changes to the code handling Settings->Account->Autoreply page. The file I changed is the following: /usr/share/roundcube/plugins/ispconfig3_autoreply/ispconfig3_autoreply.php Unfortunately it isn't into ispconfig3 project, so I can describe changes here only:

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<         $body = rcube_utils::get_input_value('_autoreplybody', rcube_utils::INPUT_POST);
---
>         $htmlenabled = rcube_utils::get_input_value('_htmlenabled', rcube_utils::INPUT_POST);
>         $body = rcube_utils::get_input_value('_autoreplybody', rcube_utils::INPUT_POST, true);
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>       if(!$htmlenabled)
>           $htmlenabled = 'n';
>       else
>             $htmlenabled = 'y';
>
>
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>           $params['autoresponder_html'] = $htmlenabled;
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>
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>             $htmlenabled = $mail_user[0]['autoresponder_html'];
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>         $htmlenabled = ($htmlenabled == 'y') ? 1 : 0;
>         if($htmlenabled == 1) $this->include_script('../../program/js/tinymce/tinymce.min.js');
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>
>         $field_id = 'htmlenabled';
>         $input_htmlenabled = new html_checkbox(array('name' =>  '_' . $field_id, 'id' => $field_id, 'value' => 1, onchange => "triggerSave()"));
>         $table->add('title', html::label($field_id, 'HTML'));
>         $table->add('', $input_htmlenabled->show($htmlenabled));
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>         $out .= "<script>function triggerSave(){ $('#rcmbtnfrm100').click(); }</script>\n";
>         if($htmlenabled == 1) $out .= "<script>tinymce.init({ selector: 'textarea#autoreplybody', menubar: false });</script>\n";

Nel file /usr/local/ispconfig/server/plugins-available/maildeliver_plugin.inc.php :
diff /usr/local/ispconfig/server/plugins-available/maildeliver_plugin.inc.php_save /usr/local/ispconfig/server/plugins-available/maildeliver_plugin.inc.php
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>                       or $data["old"]["autoresponder_html"] != $data["new"]["autoresponder_html"]
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>
>                               // Autoresponder_html
>                               $tpl->setVar('autoresponder_html', $data["new"]["autoresponder_html"]);

- Nel file /usr/local/ispconfig/interface/web/mailuser/templates/mail_user_autoresponder_edit.htm :
diff /usr/local/ispconfig/interface/web/mailuser/templates/mail_user_autoresponder_edit.htm_save /usr/local/ispconfig/interface/web/mailuser/templates/mail_user_autoresponder_edit.htm
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>                 <label for="autoresponder_html" class="col-sm-3 control-label">{tmpl_var name='autoresponder_html'}</label>
>                 <div class="col-sm-9"><input type="checkbox" value="n" id="autoresponder_html" name="autoresponder_html" onclick="AR_ResetDates();" {tmpl_var name='autoresponder_html'} /></div>
>                         </div>
>             <div class="form-group">

Unfortunately I'm a sysadmin, not a developer... So please let me know how to do this part, thanks.