ICS3 connection handshake protocol (message processing logic)

[adizere]

Closes: cosmos/ibc-rs#127
Closes: cosmos/ibc-rs#119 (already closed)

Ready for review.

The most significant part left open is adding more unit tests.

Also, in case you're wondering, the PartialEq additions in the last commit are necessary to fix integration tests (see failures here, file relayer-cli/tests/integration.rs).

Description

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For contributor use:

• Unit tests written
• Added test to CI if applicable
• Updated CHANGELOG_PENDING.md
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments
• Re-reviewed Files changed in the Github PR explorer

[codecov-commenter]

Codecov Report

Merging #188 into master will increase coverage by 21.1%.
The diff coverage is 48.9%.

@@            Coverage Diff            @@
##           master    informalsystems/hermes#188      +/-   ##
=========================================
+ Coverage    13.6%   34.8%   +21.1%     
=========================================
  Files          69      78       +9     
  Lines        3752    5038    +1286     
  Branches     1374    1714     +340     
=========================================
+ Hits          513    1755    +1242     
- Misses       2618    3076     +458     
+ Partials      621     207     -414     

Impacted Files	Coverage Δ
modules/src/context.rs	12.3% <0.0%> (ø)
modules/src/events.rs	0.0% <ø> (ø)
modules/src/ics02_client/events.rs	0.0% <ø> (ø)
modules/src/ics02_client/raw.rs	0.0% <0.0%> (ø)
modules/src/ics03_connection/error.rs	12.0% <0.0%> (-21.4%)	⬇️
...ules/src/ics03_connection/handler/conn_open_try.rs	0.0% <0.0%> (ø)
modules/src/ics03_connection/handler/verify.rs	0.0% <0.0%> (ø)
modules/src/ics04_channel/error.rs	23.0% <0.0%> (-2.0%)	⬇️
modules/src/ics04_channel/packet.rs	0.0% <0.0%> (ø)
modules/src/ics07_tendermint/client_def.rs	0.0% <0.0%> (ø)
... and 130 more

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