Move most/all block registrations to other plugins

[deathcap]

voxel-clientmc registers some of its own blocks, others it gets from other voxel.js plugins. Ideally all or most of the blocks would be provided by other plugins, to allow independent usage. See also: voxel/voxel-land#22 - for the duplicated terrain blocks (dirt, etc. - are also in voxel-land and voxel-clientmc).