Update SHH module for Whisper v6

[ConnorChristie]

What did I do?

Updated the shh module to conform to the Whisper v6 protocol. Much of the work was just changing the signatures and methods to use the new revised ones from v6.

I also added async watch functionality to the filter protocol.

If there is anything missing or additional details that need to be updated, I would be glad to make those changes!

[carver]

Looks great, thanks!

I don't know much about whisper, and after a short search could only find the v5 API docs. Would you mind linking to those docs?

I would be mostly merging blind, so I'm just going to give a thumbs up and wait a tick to see if anyone else has comments. (while you do the final linting cleanup)

The lint errors:

/home/circleci/repo/tests/core/shh-module/test_shh_key_pair.py:19:1: E302 expected 2 blank lines, found 1
/home/circleci/repo/tests/core/shh-module/test_shh_key_pair.py:36:1: E302 expected 2 blank lines, found 1
/home/circleci/repo/tests/core/shh-module/test_shh_key_pair.py:43:41: W292 no newline at end of file
/home/circleci/repo/tests/core/shh-module/test_shh_properties.py:5:1: E302 expected 2 blank lines, found 1
/home/circleci/repo/tests/core/shh-module/test_shh_filter.py:21:101: E501 line too long (114 > 100 characters)
/home/circleci/repo/tests/core/shh-module/test_shh_filter.py:24:101: E501 line too long (130 > 100 characters)
/home/circleci/repo/tests/core/shh-module/test_shh_filter.py:49:101: E501 line too long (117 > 100 characters)
/home/circleci/repo/tests/core/shh-module/test_shh_filter.py:52:101: E501 line too long (130 > 100 characters)
/home/circleci/repo/tests/core/shh-module/test_shh_filter.py:55:101: E501 line too long (114 > 100 characters)

[ConnorChristie]

I have mainly been going off of the official v6 implementation as well as the documentation from web3.js.

[carver]

Ok, thanks for the links. It partially confirmed my expectation that this is based on a (maybe) shifting API.

I hesitate a little bit to commit to our own stable version API on top of of a beta one. But... the current shh module is ridiculously outdated, it seems clear that almost no one is using it. Plus it's not a default module so 👍