Event preview alongside timer

[hopperelec]

BukkitVisibleSecondCountdown (in an upcoming commit) has functionality to append extra text alongside the "Next event:" text, and I want to use this to display an optional preview of the upcoming event. The scope of the preview and how many seconds before the event the preview should be shown should be configurable per game. Either the scope will have to be less than (or equal to) the share scope or a different countdown will have to be displayed for every player so that different events can be displayed.

[hopperelec]

This TODO will likely be fixed alongside event previews
https://github.com/HopperElec/RandomEventsPlugin/blob/4276fb67c143e75cfa95a45308aa05984d4a490f/src/main/java/uk/co/hopperelec/mc/randomevents/RandomEventsGame.java#L122