Removing assert() calls from public headers

Removed calls to assert() from public headers to have
full control when assertions are enabled in wsrep-lib
code regardless of parent project build configuration.
Moved methods containing assertions and non-trivial
code from headers into compilation units.

src/config_service_v1.cpp

@@ -23,6 +23,8 @@
 #include "wsrep/logger.hpp"
 #include "wsrep/provider_options.hpp"
 
+#include <cassert>
+
 namespace wsrep_config_service_v1
 {
     wsrep_config_service_v1_t service{ 0 };