global: implemented rudimentary memory manager to use available system memory

without forcing the OS to page swap

app/core.cpp

@@ -50,6 +50,7 @@
 #include "render/backend/opengl/opengltexturecache.h"
 #include "render/colormanager.h"
 #include "render/diskmanager.h"
+#include "render/memorymanager.h"
 #include "render/pixelservice.h"
 #include "task/taskmanager.h"
 #include "ui/style/style.h"
@@ -113,6 +114,9 @@ void Core::Start()
   // Set up the index manager for renderers
   IndexManager::CreateInstance();
 
+  // Set up memory manager
+  MemoryManager::CreateInstance();
+
   // Load application config
   Config::Load();
 
@@ -153,6 +157,8 @@ void Core::Stop()
 
   IndexManager::DestroyInstance();
 
+  MemoryManager::DestroyInstance();
+
   delete main_window_;
 }