First non-working checkin for namespaces.
[CDAP-772] Added an in-memory, non-MDS, non-persistent version of namespaces REST API. Currently part of appfabric.
[CDAP-772] First cut integration with MDS minus list all API
[CDAP-772] Added 'list all' API
[CDAP-772] Added unit tests. Removed InMemoryNamespaceMetaStore
[CDAP-772] Clean up to remove all code related to having namespaces as a separate service
[CDAP-772] Cleaned up exception handling. 'Returned' correctly from handler methods
[CDAP-772] Refactored create API to only require name in the body, not in the path
[CDAP-772] Removed unused import
[CDAP-772] Addressed some review comments.
[CDAP-772] Made create a POST API since we do not support update yet
[CDAP-772] Re-used app.meta table for namespace metadata
[CDAP-772] Created Id.Namespace and updated NamespaceMetaStore API to use it as key. Moved NamespaceMeta to cdap-proto so cdap-client and cdap-cli could use it later.
[CDAP-772] Reverted create to PUT
[CDAP-772] Addressed review comments - reduced log levels for user errors, javadoc fixes, null check fixes, etc
[CDAP-772] Addressed code review comments - reduced log levels further, used Objects.toStringHelper for NamespaceMeta#toString()
[CDAP-772] Addressed code review comments - Re-used existing store instead of adding a new NamespaceStore
[CDAP-772] Made NamespaceMeta final
[CDAP-772] Addressed code review comments - Removed unnecessary null check in getAllNamespaces. Removed unnecessary @throws clauses in javadoc. Removed trace log statements to be consistent with the rest of the handler code base.
[CDAP-772] Addressed review comments - refactored unit tests to also verify response data