CommandSenderFeature plot commands and internal queue

[NineOfGaming]

Adds an internal priority queue and support for queuing both regular commands and plot commands.

• Added a Flint-internal priority queue for important internal commands like /locate in LocateFeature.
• Added ability to send plot commands through CommandSenderFeature.
• Added public FlintAPI.queueCommand(...) and FlintAPI.queuePlotCommand(...) helpers.

[NineOfGaming]

maybe it would be better to remove the plot commands part as it might be an issue with rule 2.1d.
when i made this i was only thinking in terms of my own use case for this which that rule doesn't apply to, tho it is something that needs to be considered.