Lets the developer set a custom CGRect for the autocomplete tableview when needed

I'm trying to integrate MLPAutoCompleteTextField in a legacy codebase and I find it useful to be able to set a custom CGRect for the tableView frame. I just had to change the class methods used to create the UITableView and let them be instance methods (because the CGRect is now a property on the TextField).
If you think it could be also useful for other people, you can merge the PR.