Remove beast::Thread (RIPD-1189):

All uses of beast::Thread were previously removed from the code
base, so beast::Thread is removed.  One piece of beast::Thread
needed to be preserved: the ability to set the current thread's
name.  So there's now a beast::CurrentThreadName that allows the
current thread's name to be set and returned.

Thread naming is also cleaned up a bit.  ThreadName.h and .cpp
are removed since beast::CurrentThreadName does a better job.
ThreadEntry is also removed, but its terminateHandler() is
preserved in TerminateHandler.cpp.  The revised terminateHandler()
uses beast::CurrentThreadName to recover the name of the running
thread.

Finally, the NO_LOG_UNHANDLED_EXCEPTIONS #define is removed since
it was discovered that the MacOS debugger preserves the stack
of the original throw even if the terminateHandler() rethrows.

src/ripple/resource/impl/ResourceManager.cpp

@@ -22,8 +22,7 @@
 #include <ripple/resource/impl/Logic.h>
 #include <ripple/basics/chrono.h>
 #include <ripple/basics/Log.h>
-#include <ripple/core/ThreadEntry.h>
-#include <ripple/beast/core/Thread.h>
+#include <ripple/beast/core/CurrentThreadName.h>
 #include <condition_variable>
 #include <memory>
 #include <mutex>
@@ -114,13 +113,7 @@ public:
 private:
     void run ()
     {
-        threadEntry (
-            this, &ManagerImp::runImpl, "Resource::Manager::run()");
-    }
-
-    void runImpl ()
-    {
-        beast::Thread::setCurrentThreadName ("Resource::Manager");
+        beast::setCurrentThreadName ("Resource::Manager");
         for(;;)
         {
             logic_.periodicActivity();