Possible crash to assign tableView properties before calling `showTable`

[yoon-boom]

First of all, thank you for providing great dropdown API. I have noticed that the tableview being allocated and inserted every time showTable() being called. Inserting view could be potentially heavy lifting, how about allocate instance once in the setup() and use the UIView's hide property? Also, by fixing this, API callee can access tableview's properties (currently bug) such as background color, layer border width, etc before even it being displays.

[igongora]

I'm glad you like it!. I'll check it out your pull request and merge it after review it.