Added support to the F# API for actor objects

[jorgef]

Added spawnObj and spawnObjOpt to support creating OO actors from F#.

Usage:

spawnObj mailbox.Context "tailActor" (<@ (fun () -> new TailActor(reporter, filePath)) @>)
spawnObjOpt mailbox.Context "tailActor" (<@ (fun () -> new TailActor(reporter, filePath)) @> ) [SpawnOption.SupervisorStrategy(SupervisorStrategy.DefaultStrategy)]

This is required to create actors that are able to handle methods like PreStart() and PostStop(). Without this there is no easy way to release disposable resources at the moment.

[rogeralsing]

This has some overlap with this PR
#682

[Horusiath]

@jorgef I think, I found another solution for problem of releasing IDisposable resources with #682 (new Defer method for Actor<'t> interface). Your commit however will greatly simplify life for F#-ers, who for some reasons want to use standard Actor API for their needs.

I'll review it soon.

[Horusiath]

In this case <'Actor when 'Actor :> ActorBase> is unnecessary. Equivalent function signature is:
let spawnObjOpt (actorFactory : ActorRefFactory) (name : string) (f : Quotations.Expr<(unit -> #ActorBase)>)

This applies also to spawnObj function and documentation signatures.

[jorgef]

@Horusiath I will have a look to #682 and try to use it whenever I can.
Thanks for the review, you are right, I just improved both signatures.