thread: removed unused SwitchContext/Reschedule reason field, added missing arg parameter to SVC CreateThread

thread: moved ThreadStatus/WaitType to header, added support for arg on CreateThread, added correct CPSR reset

thread: added correct lowest thread priority, added a thread priority check, and added some comments

- cleaned up Kernel code a bit (moved stuff into namespace, fixed whitespace issues)
- added handle types for all different CTROS handles

- reorganized some kernel thread functions
- added placeholder __KernelWaitThread_Synchronization function

- added KERNEL_DEFAULT_STACK_SIZE definition (0x4000)

- added __KernelSwitchToThread for enabling a thread
- added __KernelRotateThreadReadyQueue

added a bunch of threading code, recycled from PPSSPP, with lots of hacks in for 3DS... doesn't really do much yet. Just a jumping off point