Add 'title scheduler' to allow plugins to display multiple sequential titles

[Aaron1011]

Currently, the API allows plugins to send individual Titles to plugins. However, sending a title while another title is in progress will cause one of the titles to be immediately overwritten.

Sponge should provide a utility class to allow a plugin to schedule a sequence of titles to be displayed to the client. This class would take care of scheduling titles to be sent as soon as possible, while ensuring that none of them overwrite each other.

[kashike]

The same is true with other things in the game:

• titles
• scoreboard data
• action bar

[ryantheleach]

I was thinking this was near useless honestly and that plugins could handle it themselves.

But then I realized it may be needed for cross plugin queuing.

[Aaron1011]

@kashike: I don't see how scoreboard data fits here - nothing that's displayed on a scoreboard is ephemeral the way that titles and action bar messages are.

[XakepSDK]

At least we can check, if scoreboard exists, but we can't do this with titles+action bar.