Implement methods to retrieve all anchors for one dataspace across all layer

• REST API, json representation o Anchor objects
• Java API, return a collection of Anchor(details) objects
• SPI & Impl.  Anchor getAnchors() *Anchor is PoJo not an entity class
• Use CPSException (or subclass) at source of DB exceptions
• If dataspace does not exist we well return no data (but not exception)
  TBC Need to discuss with team

Acceptance Criteria

• Conform with agreed REST API https://wiki.onap.org/display/DW/CCSDK-2870+DP%3A+CPS+REST+API+Documentation+-+PROPOSAL
• Conform with agreed Java API see https://wiki.onap.org/pages/viewpage.action?pageId=92998259 (javaDoc embedded)
• Conform with agreed SPI see https://wiki.onap.org/pages/viewpage.action?pageId=92999716 (javaDoc embedded)

? what to retrujn exactly

?what to return if databspace does not exists?