Port non-ui of Account to common

Factors the entire UI calls out of the "common" Account code by making them extension member functions and leaving them in the Android code

Successfully tested on:

• Android
• MacOS JVM target "/Applications/Android Studio Preview.app/Contents/jbr/Contents/Home/bin/java" -Dfile.encoding=UTF-8 -jar /Users/jq/dev/wally/src/build/libs/wpw.jar
• iPhone

Closes https://gitlab.com/wallywallet/android/-/merge_requests/48