Move Xor and Ior to cyclops-sum-types

[johnmcclean]

Xor in Cats has been removed in favour of Either in the Scala STD lib (see typelevel/cats#1192). That means cyclops-react is probably unique in having a sum type called Xor.

Javaslang has also made it's Either type right biased (see vavr-io/vavr#674) which lowers the value add by having an Xor type in cyclops-react.

I think there is value in having a set of lazy Either types, with in built tail recursion, in cyclops-sum-types.

Tail recursion optimization allows implementations such as https://gist.github.com/johnmcclean-aol/e2e6f549afe5031205fb25ed44002647#file-what-the-present-of-java-can-look-like-java

[johnmcclean]

Having an eager sum type is useful when implementing lazy sum types so Xor could possibly stay.

[johnmcclean]

(Lazy) Either can extend Xor in a non-core module

[johnmcclean]

Moved sum-types into the core.