Added schema files for db_cassandra module

 The schemas are for location, subscriber and version table.

utils/kamctl/dbcassandra/openser/location

@@ -0,0 +1,3 @@
+callid(string) cflags(int) contact(string) cseq(int) expires(timestamp) flags(int) last_modified(int) methods(int) path(string) q(double) received(string) socket(string) user_agent(string) username(string)
+username
+contact

utils/kamctl/dbcassandra/openser/subscriber

@@ -0,0 +1,2 @@
+username(string) domain(string) password(string) email_address(string) ha1(string) ha1b(string) rpid(string)
+username domain

utils/kamctl/dbcassandra/openser/version

@@ -0,0 +1,2 @@
+table_name(string) table_version(int)
+table_name