refactor(core-api): return all types from the /transactions/types endpoint

[spkjp]

{
    "data": {
        "Core": {
            "Transfer": 0,
            "SecondSignature": 1,
            "DelegateRegistration": 2,
            "Vote": 3,
            "MultiSignature": 4,
            "Ipfs": 5,
            "MultiPayment": 6,
            "DelegateResignation": 7,
            "HtlcLock": 8,
            "HtlcClaim": 9,
            "HtlcRefund": 10
        }
    }
}

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)