Enhanced framework support for sequential functors

Proposed Changes

use initial request to a SequentialFunctor in following transformations
- new methods nextWithContext and endWithContext
- supports start message type; no need for reflection, casting or other work-arounds
```
case class M(x: Int)
SequentialFunctor()
.start( (_: M) => Request(), Seq(ref))
.nextWithContext( (response, functorContext) =>
Request(functorContext.startMessage.x, functorContext.self)
)
.end(identity)
```
- for more context attributes, see FunctorContext or the SequentialFunctorTest
rework functor in AdminSession of fouleggs example to not get initial information via constructor but rather use a first message for the means of that
- this helps forwarding this message to the sub-functors
- this resembles the way a concurrent functor will later handle the population of initial state

[x] create a context class for any stuff that needs to be available in the transformation functions
- e.g. logging, start message, ActorContext or a selection of the attributes, failure-handling
[x] logging in transformation functions