[docker] Added signed transactions to gaiad

[greg-szabo]

Prerequisite to #723.

A little extension to the gaiad docker image: two wallets were added to the genesis file and offline transactions were created and signed between them. This allows rpc-probe to submit a transaction to the network and then create feature-rich regular RPC endpoint queries to test structs.

rpc-probe should have the following steps for testing fully populated blocks:

• locate the signed transaction in n0/c0-c1-signed.json
• Submit it to localhost:1317/txs with a POST HTTP request
• gather the Height from the response
• Submit a /block?height=<gathered_height> request to the regular RPC.

The returned block will have all fields populated and it will be easier to test the struct compatibility.

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Updated CHANGELOG.md

[codecov-io]

Codecov Report

Merging #736 (af9b5e4) into master (2b9ea0f) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #736   +/-   ##
======================================
  Coverage    42.6%   42.6%           
======================================
  Files         203     203           
  Lines       12948   12948           
  Branches     3326    3326           
======================================
  Hits         5524    5524           
  Misses       7074    7074           
  Partials      350     350           

Impacted Files	Coverage Δ
rpc/src/result.rs	27.6% <0.0%> (ø)

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