RxJS Upgrade

From RxJS 4 to 5

A cheatsheet summary of https://github.com/ReactiveX/RxJS/blob/master/MIGRATION.md

Observer is now an interface, and is implemented by Subscriber
observer.onNext('value') => observer.next('value')
subscription.dispose() => subscription.unsubscribe()
All subscriptions are composite with add and remove
flatMap => mergeMap (but flatMap still works as alias)
flatMapFirst => exhaustMap
flatMapLatest => switchMap
just => of
select => map
selectConcat => concatMap
map(function) => the same, but
map(value) => mapTo(value)