[DO NOT MERGE] minor type and syntactic changes

[sunny-g]

ethjs-schema

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Just wanted to generate conversation about other changes that might aid in schema clarity, mixed with some schema type improvements that should be updated in upstream.

You should take a look at some of the changes (namely, shh_newIdentity, shh_hasIdentity, shh_newGroup, shh_addToGroup FilterChange and SHHFilter), but can close this PR if you'd like.