Moved mergeFromCodedInputStream: to base class

Removed boiler plate.  Generated code can use the implementation of
mergeFromCodedInputStream: from the base class.  It just forwards the
call to the override of mergeFromCodedInputStream: extensionRegistry:
with an empty dictionary.
Updated generated classes to remove boilerplate

The is a followup to mergeFromCodedInputStream: change to regenerate
and unit test the protocol buffer code.
Decoupled the builders clone method from message

The clone method is more clear in its purpose, to clone the data of
this instance into a new one.  It has been decoupled from the
implementation of the generated message.
Generated classes for new implementation of clone

The unit test files have been updated to use the new implementation of
the builder clone method.
Minor updates to generated code format.
Merge branch 'move-generated-code-to-framework'