Feature/slack message bubble

[michallaskowski]

This PR adds a UIView that wraps UILabel in a sliced bubble image. To configure Slack Widget, use settings: {"name":"slack", "settings": {"apiToken":"your_token"} } It reacts to '@here', '@channel', '@everyone' mentions.

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[ochococo]

Also rebase.

[michallaskowski]

@ochococo Let's go with autolayout :)

[ochococo]

👏