Move VoteCollector into Tendermint

[foriequal0]

VoteCollector doesn't have to be generic since it is only used in tendermint. So I've removed trait Message, and SoloMessage which is its dummy implementation.

[majecty]

Good! I have wanted this patch!

[foriequal0]

I have to resolve the warning.

error: large size difference between variants
  --> core/src/consensus/stake/actions.rs:66:5
   |
66 | /     ReportDoubleVote {
67 | |         message1: ConsensusMessage,
68 | |         message2: ConsensusMessage,
69 | |     },
   | |_____^
   |
   = note: `-D clippy::large-enum-variant` implied by `-D warnings`
help: consider boxing the large fields to reduce the total size of the enum
  --> core/src/consensus/stake/actions.rs:66:5
   |
66 | /     ReportDoubleVote {
67 | |         message1: ConsensusMessage,
68 | |         message2: ConsensusMessage,
69 | |     },
   | |_____^
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant

[foriequal0]

The test is flaky. I'll rebase and merge it.