Update to tendermint-rs v0.16

[ebuchman]

Currently using tendermint-rs v0.15.

v0.16 includes minor changes, but two in particular that affect us:

1. Removed the lite module (we need to change all references to point to the light_client crate now)
2. Updated and removed some crypto dependencies (Replace signatory with ed25519-dalek and k256 crates tendermint-rs#522 (review))

Tendermint-rs v0.17 is a work in progress with lots of breaking changes from the proto stuff. We should upgrade to v0.16 first to deal with the breaking changes from (1) independently. Looks like this will be a bunch of work and will require some refactoring of the relayer crate

We need the changes from (2) to get signing working, ie. to merge the code from #242 into the relayer-cli

Could probably use help from @romac / @ancazamfir on this one

[romac]

I will take care of this as part of #90.