Make ReactiveDerivedCollection schedulable

By default, the scheduler is Scheduler.Immediate, so no change from the current behavior
Autogenerate a WhenAny overload that automatically creates tuples for you
Merge pull request #643 from reactiveui/autogenerate_WhenAny_Tuple

Autogenerate a WhenAnyValue overload that automatically creates tuples for you
Merge pull request #642 from reactiveui/make_derived_collection_schedulable

Make ReactiveDerivedCollection schedulable
Add a ReactiveContentPage<T> as well
Merge branch 'rxui6-master' of github.com:reactiveui/ReactiveUI into rxui6-master
Add a Command method more familiar to the TPL proletariat
Add Cancellation-friendly versions of CreateAsyncTask
Hide poorly designed ICommand methods
Just for you, @onovotny <3
Someday I will be good at Fluency
Add in RxUI 5.x ReactiveCommand for compatibility purposes
These methods are just :trollface:ing, make people use Task.Run
Merge pull request #645 from reactiveui/command-improvements

Finish up ReactiveCommand
Fix WinRT derp
Test scheduling
Get the tests to compile not really RIP me
Fix up WinForms build
Merge branch 'rxui6-master' into add_delay_change_notifications_to_RO
Revert "Hide poorly designed ICommand methods"

This reverts commit 19c64700474a747e123d22198dd076cef8e776b3.