I don't want a dependency on JodaTime for my projects, so I decided to start fixing #131

TODO:
[x] Common library
[x] MySQL
[x] Fix TimestampEncoder
[ ] Fix MySQL tests
[] Postgres
[] Fix Postgres tests

Looking for comments on this before I finish the whole thing (ideally from someone who has in depth knowledge of java.time) - I'm not 100% sure I've converted the calls successfully in some cases. Mostly followed this as a guide: https://blog.joda.org/2014/11/converting-from-joda-time-to-javatime.html

Implementation notes:
TimestampEncoder is definitely broken, probably need to use ZonedDateTime instead of LocalDateTime etc. Will take a look at it later and resolve. Even though TimestampEncoder assumes no time zone, it formats times using a 'Z' suffix to represent the UTC timezone. As such, I had to make it use ZonedDateTime otherwise a formatting exception would occur at runtime.

Cheers