MXS-2008 Provide single entrypoint for initializing maxbase

Everything of maxbase can now be initialized by a call to

    maxbase_init();

(from a C-program) or

    maxbase::init();

from a C++-program and finalized with calls to either
maxbase_finish() or maxbase::finish(). Creating an instance
maxbase::MaxBase will take care of both operations.

maxutils/maxbase/src/CMakeLists.txt

@@ -3,6 +3,7 @@ add_library(maxbase STATIC
   eventcount.cc
   log.cc
   logger.cc
+  maxbase.cc
   messagequeue.cc
   semaphore.cc
   stopwatch.cc