build: Enabling -Werror in debug mode and fixing discovered issues

Change-Id: I29685dcb9240a3e0c8d7eaf28c8bc2ae720e55a1
diff --git a/daemon/table/cs.hpp b/daemon/table/cs.hpp
index e4c1ae6..aeaec38 100644
--- a/daemon/table/cs.hpp
+++ b/daemon/table/cs.hpp
@@ -85,7 +85,7 @@
    *  Reference: "Skip Lists: A Probabilistic Alternative to Balanced Trees" by W.Pugh
    *  \return{ returns random layer (number) in a skip list}
    */
-  int
+  size_t
   pickRandomLayer() const;
 
   /** \brief Inserts a new Content Store Entry in a skip list