Allow absolute paths

hello, I had problems on my production server with relative paths - so i made some quick changes to allow absolute paths in config / tinyMce init, like this:
```
    open_manager_upload_path: '<?php echo $_SERVER['DOCUMENT_ROOT'];?>/uploads/',
```
(don't know if this is needed too - it probably is:
```
    relative_urls : false,
```
)

it's just a quinck patch, not fully tested (it works for me, so it was enough at the time)

Some refactoring might be needed. But sharing anyway is probably better than keeping it for me :)