ChatInputBar won't appeal to constraints

I just want to use the ChatInputBar, but I can't get it to stick properly to the bottom of the screen.

Here's what I do:
```
chatInputView = ChatInputBar.loadNib()
var appearance = ChatInputBarAppearance()
appearance.sendButtonAppearance.title = NSLocalizedString("Send", comment: "")
appearance.textInputAppearance.placeholderText = NSLocalizedString("Type a message", comment: "")
chatInputPresenter = BasicChatInputBarPresenter(chatInputBar: chatInputView, chatInputItems: self.createChatInputItems(), chatInputBarAppearance: appearance)
chatInputView.maxCharactersCount = 280
self.view.addSubview(chatInputView)
```

I tried adding my own constraints, but that just breaks things.

Start with the ChatInputBar.loadNib and BasicChatInputBarPresenter setup shown in the report, then inspect how the loaded view participates in Auto Layout. Reproduce the reported setup and verify that the ChatInputBar remains anchored to the bottom of the screen without breaking constraints.

Written by the indexing model from the issue text.