changing to static factory methods for Comment
supress warnings for unchecked cast on cache use moved to variable declaration
Adding abstract API4KB classes

Builder pattern is used for Environments
abstract classes in api4kb

some method implementations are moved to the abstract classes for reuse.
adding AbstractKnowledgeEncoding

plus some refactoring
Merge branch 'static-factory-exp'

* static-factory-exp:
  adding AbstractKnowledgeEncoding
  abstract classes in api4kb
  Adding abstract API4KB classes
  supress warnings for unchecked cast on cache use moved to variable declaration
  changing to static factory methods for Comment