Add ForwardingViewer

[MrHell228]

SpongeAPI | Sponge

ForwardingViewer is some kind of extension of kyori ForwardingAudience idea to sponge Viewer

ForwardingViewer:

• of(viewersSupplier) is general method to support basically any custom viewers
• of(Collection<Viewer>) and of(Viewer...) are easy shortcuts for static groups of viewers
• allAround(world, center, radius) and allAround(entity, radius) are dynamic

Viewer:

• Removed spawnParticles() that took radius
• Added (x, y, z) variants for spawnParticles, playMusicDisc and stopMusicDisc, made their (position) variants defaulted
• Updated some descriptions