Remove joda time

[jisantuc]

Overview

This PR removes joda time, since @pomadchin worked the DateTimeFormat magic for us to get by without requiring the dep (and even added more format unit tests).

Checklist

• New tests have been added or existing tests have been modified
• Changelog updated

Addresses #150
Replaces #152

[jisantuc]

I can't approve because I opened it but @pomadchin feel free to merge with a changelog entry

[pomadchin]

For the context (if there would be any questions about the joda-time dep in general and why it disappeared from modern libs): https://github.com/JodaOrg/joda-time#joda-time

Joda-time is no longer in active development except to keep timezone data up to date. From Java SE 8 onwards, users are asked to migrate to java.time (JSR-310) - a core part of the JDK which replaces this project. For Android users, java.time is added in API 26+. Projects needing to support lower API levels can use the ThreeTenABP library.

It is mostly not recommended to have joda-time in deps of a new project.

[pomadchin]

According to STAC Docs, it follows RFC3339, that is why we need an RFC3339 compatible ISO Formatter. Such formatter description is described in this SO post.

Also a nice post that explains ISO formatter implementation in Java