The method 'getoffer' should support looking up a user's open-offers, and other users' available offers.
- Adjust api-beta-test-guide.md to use only 'getoffer'.
- Adjust trade simulation scripts to use only 'getoffer'.
- Adjust api testcases to use 'getoffer' in place of 'getmyoffer'.
- Mark appropriate methods and protobuf msgs as deprecated.
The test harness is compatible with bitcoin-core 0.19, 0.20, 0.21.
Also removed some unnecessary comments about registering dispute
agents in the test harness because it now happens by default.
The codacy issue "$/${} is unnecessary on arithmetic variables"
seems to not apply to $(echo $((1 + $RANDOM % 10))), but we
try another syntax to make her happy.
The script demonstrats a way to always keep one offer in the market.
As soon as the offer is taken and the trade is completed, another
offer is placed.
