Upgrade to Java 8 Time API

[NaanProphet]

After we write more tests, I thought it might be more intuitive if we moved away from the old Calendar API and used the new java.lang.time classes. Any concerns?

[florianmski]

Problem is I build this tool at first to use it in an Android app and you can't use Java 8 on Android yet 😢
What about using a backport?

[NaanProphet]

LOL that is awesome ;)

backport sounds like a great alternative! And if in the meanwhile, Android finally supports Java 8 then we'd have a seamless transition.

This is going to be fun