Fix warnings in core and common

chunk_file: General cleanup

Use the citra user path for the sdmc directory

- Remove unnecessary ifdefs
- Remove commented out code. Can be retrieved later if needed.

Implement filesystem services, and the required kernel objects.

Core: Replace a sprintf in core_timing with StringFromFormat

Core: Get rid of unnecessary switch statement in Kernel

Core: Fix warnings in gpu.cpp

Small, general code cleanup 

Digital user input and HID module implementation for PAD

loader.cpp: improved file extension checking, made Upper/LowerStr useful, moved string_util into Common namespace

Prune redundant includes

Removed fixed_size_queue.h

Common: Fix a potential infinite loop in StringUtil's ReplaceAll

Common: Remove HAVE_CXX11_SYNTAX define from Common.h

It's unused and doesn't look like it compiles anyway :/

Instead of forcibly taking the last 4 characters, it now finds the last extension separator (the period) and takes a substr of its location.