Diagnose API23 crash issue

Zero in on the web3j code that is crashing when we use API23.

1. Reproduce: Ran an API23 emulator and run the app. It will crash, probably in ticker service when it tries to call the smart contract.
2. Make it work: Use an older version of web3j (maybe 4.6.0-android or 4.2.1-android). You will have to remove the web3j library dependency and restore the web3j import from Maven. You may have to resolve (or remove eg the 1559 transactions).
3. Make it work using the local web3j builds. Use this repo: https://github.com/AlphaWallet/web3j follow the build instructions and copy the abi library into the alpha-wallet-android project.
4. Work out which part of web3j is the culprit, and see if it's possible to back-port just that code (that is, a mix of the forked web3j on the AW repo and the old web3j source).

This may be just a write-up, but ultimately if you can solve the issue it would be very valuable.