591: Problem: no transaction type for joining validator set (CRO-553) r=tomtau a=tomtau

Solution:
- consolidated ABCI node state to have one field dedicated to validate state tracking
- added a NodeJoinTx type + basic validation code and tests
- added a End block handling when the validator power changed or new nodes were changed -- based on the top validators after modifications, it computes the validator updates it needs to pass to tendermint
- small steps in storage/tx.rs refactoring -- two verify functions to distinguish between abci-only and enclave-dependant transactions + moved out the huge functionality tests into a separate file

NOTE: don't get scared about the PR size -- most of it is just moving `storage/tx.rs` tests into a separate file (it'll still need some improvements, but that can be done in a separate PR)


593: Problem: (CRO-582) Create transfer address is not re-usable r=tomtau a=calvinlauco

Solution: Extracted MultiSigAddress from root_hash service to serve single responsibility

---
Remarks:
- This PR is a pre-requisite of the JS library by making components re-usable by JS
- Removed n(total_signers) field because it is implied from len of public keys

Co-authored-by: Tomas Tauber <2410580+tomtau@users.noreply.github.com>
Co-authored-by: Calvin Lau <calvinlauco@gmail.com>

593: Problem: (CRO-582) Create transfer address is not re-usable r=tomtau a=calvinlauco

Solution: Extracted MultiSigAddress from root_hash service to serve single responsibility

---
Remarks:
- This PR is a pre-requisite of the JS library by making components re-usable by JS
- Removed n(total_signers) field because it is implied from len of public keys

598: Bump abci from 0.6.3 to 0.6.4 r=tomtau a=dependabot-preview[bot]

Bumps [abci](https://github.com/tendermint/rust-abci) from 0.6.3 to 0.6.4.
<details>
<summary>Changelog</summary>

*Sourced from [abci's changelog](https://github.com/tendermint/rust-abci/blob/develop/CHANGELOG.md).*

> ## v0.6.4
> 
> ### IMPROVEMENTS:
> 
> - [\#100](https://github-redirect.dependabot.com/tendermint/rust-abci/pull/100): worker panic propagated to the abci process
> 
> _November 11, 2019_
</details>
<details>
<summary>Commits</summary>

- See full diff in [compare view](https://github.com/tendermint/rust-abci/commits)
</details>
<br />

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Co-authored-by: Calvin Lau <calvinlauco@gmail.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>