Kernel: Implement supplementary groups

This code has very ugly file parsing code. I have to create API
for reading files line by line in kernel space...

This allows users to open framebuffer/input files without root.

Mounting has to be moved to userspace soon. It makes no sense to
hard code permissions for every (device) file.

kernel/CMakeLists.txt

@@ -14,6 +14,7 @@ set(KERNEL_SOURCES
 	kernel/APIC.cpp
 	kernel/BootInfo.cpp
 	kernel/CPUID.cpp
+	kernel/Credentials.cpp
 	kernel/Debug.cpp
 	kernel/Device/Device.cpp
 	kernel/Device/FramebufferDevice.cpp