Deprecate Sponge mechanic with note to use CraftBook 5

[me4502]

Is your feature request related to a problem? Please describe. The sponge mechanic is duplicated across both WorldGuard and CraftBook, with CraftBook having a more feature-complete version. This also doesn't fit into WG as well as it does to CB.

Describe the solution you'd like Deprecate for removal in WG8, with a note to use CB5 instead.

Describe alternatives you've considered Stay as-is I guess

Additional context Ideally, CraftBook5 is in a mostly-complete beta or public release state by the time WG8 rolls around, but it doesn't overally matter.