Some minor fixes

[Some css fix](https://github.com/denis0706/Redux-Framework/blob/20ca4c4ae965a002237d6fe9464c45b0b47c8aef/options/css/options.css#L791-L793) - center wp 3.5 color picker with description

[Fix src attribute for Upload field](https://github.com/denis0706/Redux-Framework/blob/20ca4c4ae965a002237d6fe9464c45b0b47c8aef/options/fields/upload/field_upload.js#L7)

[L28](https://github.com/denis0706/Redux-Framework/blob/master/options/validation/url/validation_url.php#L28) I have found, that some server doesn't include filter extension in php config. So some users who don't have knowlegde how to setup server or haven't permission to change config can get undefined function 'filter_var' error while saving their redux options. I don't think that my workaround is solution. I'm not good at reg expression, so maybe someone can change filter_var function with reg exp -  I think it would be the best solution