Fixed issues noted on Github.

More accurate naming for GitnuFileSystem class

Refactor of the existing codebase.

Design using 4 primary classes.
- GitnuTerminal --> terminal display.
- FileHandler --> file system ops.
- Git --> TBC Git operations.
- Gitnu --> wrapper class for all operations.

Newline at the end of file.

Fixing review notes, adding Figlet produced logos.

Tidied up css files.

Cleaned up terminal display, cleaned up file structure. Tried to treat terminal.dart as it's own library file and not edit where possible.

BUG=
R=koz@chromium.org

Review URL: https://codereview.appspot.com/43160043
Merge branch 'master' of https://github.com/camfitz/gitnu