Adds 404error handler, Fixes .html, .scss and sets https optional in some cases

This PR:

- Sets the HTTPS optional (it won't redirect users to *https* if requesting *http*) for everything except the API;

- Fixes identation on `Gruntfile`, some `.scss` files and also `.hbs / .html` files;

- Removes additional `<html>` on top of some `.html` files, which lead to duplicated *html* tag (which invalidates the html);

- adds `404 error` error handling (needs to create a beautiful 404 page)