Tho Pham

@TheBogueRat @John-Connolly I made showMenu() and hideMenu() public so that you guys can control behavior of dropdown menu more flexible :) Please feel free to reopen this if you guys...

@ins0u make sure `menuView` didn't be deallocated before using menuView.hideMenu(). Putting menuView.hideMenu() in `viewDidDisappear(_:)` is one of the reasons might cause the crash.

@adamhartford this is a good PR and I like the idea of showing images in dropdown cells. But I'm thinking about making this generic, meaning that users can custom dropdown...