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/fw/strategy.hpp b/daemon/fw/strategy.hpp
index 570f219..4c9a2e5 100644
--- a/daemon/fw/strategy.hpp
+++ b/daemon/fw/strategy.hpp
@@ -29,8 +29,7 @@
 #include "forwarder.hpp"
 #include "table/measurements-accessor.hpp"
 
-namespace nfd {
-namespace fw {
+namespace nfd::fw {
 
 class StrategyParameters;
 
@@ -480,8 +479,7 @@
   }
 };
 
-} // namespace fw
-} // namespace nfd
+} // namespace nfd::fw
 
 /** \brief Registers a strategy
  *