Associate anchor to schema set

- db schema updated
- db layer tests provided for ancor create and reading by dataspace
- anchor model is removed from rest api as extra
- api/spi updated to use string references instead of object

Issue-ID: CPS-99
Change-Id: Ideeb83fa9e91ec1816308d8327a6589b999c64c5
Signed-off-by: Ruslan Kashapov <ruslan.kashapov@pantheon.tech>
diff --git a/cps-ri/src/test/resources/data/clear-all.sql b/cps-ri/src/test/resources/data/clear-all.sql
index 3d93825..522f9e6 100644
--- a/cps-ri/src/test/resources/data/clear-all.sql
+++ b/cps-ri/src/test/resources/data/clear-all.sql
@@ -1,3 +1,4 @@
+DELETE FROM FRAGMENT;
 -- clear all via dataspace table cleanup
 -- all other data will be removed by cascade
 DELETE FROM DATASPACE;