Eliminate PartialDelegatingField (in favor of NestedField).

One test is failing.
Move the implicit PortableField.toSome conversion to object ImplicitConversions.

This should help making the code be less surprising.
Minor improvements to debugging experience.
Fix bug in NestedField of the updated subject.

This affected cases where multiple fields operated in succession.
Add FieldWithDelegates.
Optimized code that showed up as a hotspot on Android.

There were issues with a bunch of "flatMap" class constructors
and calls to packageNamesToExcludeForOriginToString.
Made TargetedField.withSetter not have unused wrapping.
Report errors that happen in an urgentFuture.

Add PortableValue.nothing to be used when a PortableValue is required, but no value is available.
Optimize TypedFieldSeq by using a List for the fields.

This is good since the fields never change and are only accessed sequentially.
Before, with the Vector, the stack trace would include the following
since not using LinearSeqOptimized (notice all of the foldLeft's):

08-08 15:30:17.878: E/sample_application(335): 	at com.github.triangle.TypedFieldSeq$$anon$2$$anonfun$attempt$1.apply(TypedFieldSeq.scala:45)
08-08 15:30:17.878: E/sample_application(335): 	at com.github.triangle.TypedFieldSeq$$anon$2$$anonfun$attempt$1.apply(TypedFieldSeq.scala:43)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:143)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:143)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.Iterator$class.foreach(Iterator.scala:772)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.immutable.VectorIterator.foreach(Vector.scala:648)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.IterableLike$class.foreach(IterableLike.scala:73)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.immutable.Vector.foreach(Vector.scala:63)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.TraversableOnce$class.foldLeft(TraversableOnce.scala:143)
08-08 15:30:17.878: E/sample_application(335): 	at scala.collection.immutable.Vector.foldLeft(Vector.scala:63)
08-08 15:30:17.878: E/sample_application(335): 	at com.github.triangle.TypedFieldSeq$$anon$2.attempt(TypedFieldSeq.scala:43)
08-08 15:30:17.878: E/sample_application(335): 	at com.github.triangle.TypedFieldSeq$$anon$2.attempt(TypedFieldSeq.scala:37)