Release wallet-2.2.0

[ValuedMammal]

Opening this issue to keep track of PRs that can be included in the wallet-2.2.0 release. Backporting a fix or feature will essentially involve cherry picking the necessary commits from a merged PR and opening a new PR to the release/2.2 branch.

• Backport #300 - Add utilities to test persistence #311
• Cherrypick #306 onto release/2.2 #309