Abstract away filesystem writes.

[KrishKayc]

The app directly writes to files and creates directories. Example saveSite() => os.MkdirAll, iouti.WriteFile.

We need to abstract away these file writing and directory creation into an interface. (Ex: Writer, FSHandler etc..)

This will help in unit test being independent of filesystem and faster unit tests in general (From unit tests, we can use our mock fswriter)