Port reorder column from ngDataTable.

[alwasa0b]

I ported the current reorder column functionality from the primeng project.

[mertsincan]

Thank a lot for PR, @alwasa0b. I'll review and get back to you.

[alwasa0b]

This seems to have broken the Column Toggler demo. That is because I am keeping a variable to hold the reordered columns within the DataTable.js. I am not sure how you want to go about that. I can think of few option to go about it.
First option, would be a callback function to update the column array with the new order when onDrop is done. Second option is to move the Multi-Select toggle to the DataTable.js. Lastly, require the column array to be passed for some of the functionalities to work.

[cagataycivici]

Please monitor at #81

We can't merge it but will consult to it during our implementation which is very soon.