Add getNrgPrice Java API call.

[aionick]

Description

Please include a brief summary of the change that this pull request proposes. Include any relevant motivation and context. List any dependencies required for this change.

• The NrgOracle class provides a method to recommend a user an energy price to use, so far only web3 API gives access to this and not Java API. I've added a call to the Java API to access this value. See my other PR in the aion project for the rest of this functionality.

Fixes Issue # N/A.

Type of change

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• Bug fix.
• New feature.
• Breaking change (a fix or feature that causes existing functionality to not work as expected).
• Requires documentation update.

Testing

Please describe the tests you used to validate this pull request. Provide any relevant details for test configurations as well as any instructions to reproduce these results.

• I added a test to the BaseAPITest. Ran through it in debugger a few times.

Verification

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• I have self-reviewed my own code and conformed to the style guidelines of this project.
• New and existing tests pass locally with my changes.
• I have added tests for my fix or feature.
• I have made appropriate changes to the corresponding documentation.
• My code generates no new warnings.
• Any dependent changes have been made.