Persist chosen units across app restarts

[kaloudis]

Description

Relates to issues: ZEUS-1417, ZEUS-1580, ZEUS-1527, ZEUS-1871

The primary purpose of this PR is to ensure that chosen units persist across app restarts. This is particularly helpful for shops that ring up sales based in fiat currencies.

This PR also makes a change to AmountInput that ensures that the units are not reset when a generated invoice is cleared (hitting the X button).

As a result, I believe ZEUS-1580 is now resolved.

I've also ensured that ZEUS-1527 and ZEUS-1871 remain corrected.

This pull request is categorized as a:

• New feature
• Bug fix
• Code refactor
• Configuration change
• Locales update
• Quality assurance
• Other

Checklist

• I’ve run yarn run tsc and made sure my code compiles correctly
• I’ve run yarn run lint and made sure my code didn’t contain any problematic patterns
• I’ve run yarn run prettier and made sure my code is formatted correctly
• I’ve run yarn run test and made sure all of the tests pass

Testing

If you modified or added a utility file, did you add new unit tests?

• No, I’m a fool
• Yes
• N/A

I have tested this PR on the following platforms (please specify OS version and phone model/VM):

• Android
• iOS

I have tested this PR with the following types of nodes (please specify node version and API version where appropriate):

• Embedded LND
• LND (REST)
• LND (Lightning Node Connect)
• Core Lightning (c-lightning-REST)
• LndHub
• [DEPRECATED] Core Lightning (Spark)
• [DEPRECATED] Eclair

Locales

• I’ve added new locale text that requires translations
• I’m aware that new translations should be made on the ZEUS Transfix page and not directly to this repo

Third Party Dependencies and Packages

• Contributors will need to run yarn after this PR is merged in
• 3rd party dependencies have been modified:
  • verify that package.json and yarn.lock have been properly updated
  • verify that dependencies are installed for both iOS and Android platforms

Other:

• Changes were made that require an update to the README
• Changes were made that require an update to onboarding

[shubhamkmr04]

tACK