Common code folder changes

- Changed folder name qcommon to common
- Changed header qcommon.h to common.h
- Changed header qfiles.h to files.h
- Change qcommon_* functions to Com_* functions
Common init changes.

- Don't require argc / argv processing on in init, use
Com_ParseCommandLine, Com_InitArgv.  This makes the API cleaner when
dealing with non-argv based startups (e.g. Android)
- Updated affected files.