1. Added KeyValueStore.Iterate for implementing the different List, ListV2 etc. implementations. This allows for more efficient use of memory depending on the situation.
2. Implemented an inmemory teststore for running tests. This should allow to replace MockKeyValueStore in most places.
3. Rewrote tests
4. Pulled out logger from bolt implementation so it can be used for all other storage implementations.
5. Fixed multiple things in bolt and redis implementations.
* Refactor List in Pointer DB
* Fix pointerdb-client example
* Fix issue in Path type related to empty paths
* Test for the PointerDB service with some fixes
* Fixed debug message in example: trancated --> more
* GoDoc comments for unexported methods
* TODO comment to check if Put is overwriting
* Log warning if protobuf timestamp cannot be converted
* TODO comment to make ListPageLimit configurable
* Rename 'segment' package to 'segments' to reflect folder name
