Commit for review - Multiple pages in designer

This pull request includes work I've done so far for managing multiple pages from the Designer. Please review the code and give feedback on what has been so far. Meanwhile, I'll continue to complete the functionalities.

Signed-off-by: Bimal Yashodha <kb.yashodha@gmail.com>
Rather than passing `configuration storage database` and `pdf_pages table` names as part of the request, use
```php
PMA_Util::backquote($cfgRelation['db']) . "." . PMA_Util::backquote($cfgRelation['pdf_pages'])
```