Bring Nimbus Verified Proxy into status-go

[dlipicar]

Bringing this into status-go
Ideally, we want to use Nimble to get nim dependencies build them and track their version. nwaku and nim-sds use nimbus-build-system so we couldn't go this way at that moment (it's changing though). Anyway, if Nimble is availble - go with it. Otherwise...

... clone the repo with status-go. Not a git submodule, but clone. Follow NIM_SDS_SOURCE_DIR in status-go Makefile.