Replace the unclear MakeDecider with clearer versions

Akka JVM has `SupervisorStrategy.makeDecider` functions of which one has been ported to our code.

    SupervisorStrategy.MakeDecider(exceptions)

When you see the line above in the code it is very unclear, just by looking at the name, what it does.
It returns _Restart_ if the reason to why an actor failed is one of the specified exceptions; otherwise _Escalate_ .

A more suitable name would probably have been something like

    SupervisorStrategy.MakeRestartDeciderFor(exceptions).

However in our code base it's only used twice, and the usage looks like this:

    SupervisorStrategy.MakeDecider(typeof(Exception))

Which means, always Restart. This commit replaces those calls with the much clearer

    reason => Directive.Restart

And also removes `MakeDecider`.

If we want to introduce helper functions for making deciders we should not port Akka JVMs way, but introduce our own.

Thoughts?