Support 'HTTP-Problem' in API response

[spikeekips]

The detailed specification of 'HTTP-Problem' can be found in https://tools.ietf.org/rfc/rfc7807.txt .

[Geod24]

Given that:

• the APIs are still being developed
• this has little impact on the core of our product
• the ROI is pretty low

I moved this to the MainNet milestone

[kfangw]

@cmcm2222 May I take this issue if you don't mind?

[johndoe0x]

@kfangw of course. why not?

[kfangw]

https://github.com/moogar0880/problems

[spikeekips]

Good job @kfangw