Update submodules (#4727)

Closes #4708

This updates jsoncpp, mbedtls, TCLAP and SQLiteCpp to their latest stable release. A few additional changes were needed:

* jsoncpp deprecated Reader, FastWriter and StyledWriter which I've replaced
  with some helper functions in JsonUtils.cpp

* SQLiteCpp changed how it builds with external sqlite libraries, now expecting
  them to be installed. The simplest path was to remove sqlite from cuberite's
  submodule and just use SQLiteCpp's internal version.

src/CompositeChat.cpp

@@ -6,6 +6,7 @@
 #include "Globals.h"
 #include "CompositeChat.h"
 #include "ClientHandle.h"
+#include "JsonUtils.h"
 
 
 
@@ -408,11 +409,10 @@ AString cCompositeChat::CreateJsonString(bool a_ShouldUseChatPrefixes) const
 
 	#if 1
 		// Serialize as machine-readable string (no whitespace):
-		Json::FastWriter writer;
-		return writer.write(msg);
+		return JsonUtils::WriteFastString(msg);
 	#else
 		// Serialize as human-readable string (pretty-printed):
-		return msg.toStyledString();
+		return JsonUtils::WriteStyledString(msg);
 	#endif
 }