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>
`db` is not a valid attribute of <form> element. Use 
```php
$html .= PMA_URL_getHiddenInputs($GLOBALS['db']);
```
to include db and token as hidden inputs.