procfs and task/process bookkeeping improvements

[arihant2math]

Keeps track of utime and stime on both the process and task level. It exposes these values via sys_clock_gettime timers and also through procfs.

Also this PR splits procfs into multiple files and abstracts out some common code (i.e. implementing Inode for simple files, etc.). It also adds support for viewing task details via task and fd details fd_info.

TODO:

• Properly distinguish between whether task stats or process stats should be shown when tgid == tid. Currently /proc/<pid>/task/<pid> displays thread group uptime statistics instead of task uptime statistics.
• Fix hanging when calling ls on fd_info.