refactor(core-state): wallet model cleanup

[spkjp]

This PR cleans up the wallet model and moves almost all of the existing wallet properties into a private attributes object.

Whenever the wallet model had to be extended we'd introduce a new property. This bloated the entire class with no clear semantic structure. With more and more transaction types coming up. this becomes even more of an issue.

The new approach to interface with (custom) wallet data is by using the following set of functions:

    hasAttribute(key: string): boolean;
    getAttribute<T = any>(key: string, defaultValue?: T): T;
    setAttribute<T = any>(key: string, value: T): void;
    forgetAttribute(key: string): void;

Internally it is using dottie to support access based on a property path.

This PR is quite pervasive and will break at least all existing custom transactions and #2773.

What kind of change does this PR introduce?

• Bugfix
• Feature
• Refactor
• Performance
• Tests
• Build
• Documentation
• Code style update
• Continuous Integration
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

Does this PR release a new version?

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the develop branch, not the master branch
• All tests are passing
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)