Refactor and modernize namespace declarations

Move all unit tests to namespace nfd::tests

Delete unused header core/algorithm.hpp

Change-Id: I5591f0c5f3bb5db67f8b45fae95471f8a555ca68
diff --git a/daemon/face/websocket-transport.cpp b/daemon/face/websocket-transport.cpp
index 2d118ec..df7b36b 100644
--- a/daemon/face/websocket-transport.cpp
+++ b/daemon/face/websocket-transport.cpp
@@ -26,8 +26,7 @@
 #include "websocket-transport.hpp"
 #include "common/global.hpp"
 
-namespace nfd {
-namespace face {
+namespace nfd::face {
 
 NFD_LOG_INIT(WebSocketTransport);
 
@@ -174,5 +173,4 @@
   this->setState(TransportState::CLOSED);
 }
 
-} // namespace face
-} // namespace nfd
+} // namespace nfd::face