Prepare cardano-sl/wallet for the release 1.5

[KtorZ]

Context

We've frozen development on cardano-sl/wallet some times ago. However, the branch has been left partly "abandoned" and we've only taken care of applying bug fixes to this. Still, integration tests aren't available on cardano-sl/wallet and we haven't quite controlled whether it indeed includes all the patches from 1.4.x.
Also, there are maybe a few things to review from the API documentation and the build instructions.

Decision

All-in-all, we need to spend time on this figuring out what's in for the release, what's missing, and document it.

Acceptance Criterias

1. Integration tests must be enabled on cardano-sl/wallet, at least locally
2. All (relevant) patches from 1.3.x & 1.4.x must be listed
3. All (relevant) patches from 1.3.x & 1.4.x must have been applied to cardano-sl/wallet
4. A clear inventory of the features, fixes & improvements currently present in cardano-sl/wallet must be established and documented as part of the CHANGELOG
5. Undesired features present in cardano-sl/wallet (and added since 1.4) may be removed.

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Development Plan

• I intend to finalize cleanup of cardano-sl for anything externally-owned wallets or BIP-44 related
• I intend to revert some commits about decoupling that happened in the wallet (the bits removing the NodeStateAdaptor in favor of the NodeClient)
• I intend to backport the wallet integration tests on cardano-sl (solving "merge" conflicts on sl)
• I intend to make a full list of changes and PR we merged on sl since 1.4.0 and that will be included in 1.5.0

PR

Number	Base
input-output-hk/cardano-sl#4045	develop
input-output-hk/cardano-sl#4046	develop
input-output-hk/cardano-sl#4047	develop
input-output-hk/cardano-sl#4054	develop
input-output-hk/cardano-sl#4051	develop

QA

Criteria	Coverage
1.	Integration tests have been backported and merged into develop (cf input-output-hk/cardano-sl#4047) and they even run in the hydra CI https://hydra.iohk.io/build/588876/log 🎉
2. 3. 4.	CHANGELOG added to reflect the actual history on cardano-sl/develop input-output-hk/cardano-sl#4054
5.	Remaining PRs have cleaned-up a few things that had either incorrectly made to develop or, needed some tweaking (like, making the new node monitoring API optional and disable by default, to preserve the existing behavior).

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Retrospective

[piotr-iohk]

LGTM 👍