Improved submodules

PluginManager is now a submodule
PluginManager::AddDirectory no longer returns bool
Made Initialize/Uninitialize static methods from non-submodules private
Fixed PluginManager initialization
Fixed cpuid reported supported on unsupported compilers
Added some CPU vendors
Updated MemoryManager

Renamed MemoryLeakTracker[.hpp|.cpp] to MemoryManager[.hpp|.cpp]
Added MemoryManager::GetAllocatedBlockCount()
Added MemoryManager::GetAllocatedSize()
Optimized MemoryManager (no longer allocates a time buffer)
Fixed leak from UberShaderPreprocessor