Replace deprecated SDL APIs

Replace deprecated SDL SdlInstance usage with xapp-frame's SdlStorage
APIs, which have been built on top of the valid SDL SyncStorage APIs.
Upgrade SDL version to v0.8.0.

Issue-Id: RIC-805

Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I04142853f74775ae40b71a0bef5431508acbb61a
diff --git a/RELNOTES b/RELNOTES
index 7aef394..5ca454a 100644
--- a/RELNOTES
+++ b/RELNOTES
@@ -1,3 +1,6 @@
+### v0.10.8
+* Replacing deprecated SDL APIs
+
 ### v0.10.7
 * Xapp-frame version update
 * Dockerfile correction for test applications