Add wrapper_tag arg and wrapper_class arg in wp_pagenavi function

[Mahjouba91]

Hello,

I wanted to have more control on the Markup of the plugin so I decided to add two args in order to allow developers to update the main wrapper "

, with those two new args, you can replace the div tag and the class name.

Hope you can merge this thing, by the way sorry for the issue with the strange indentation in my code.