fix for the Link issue

[kalwalt]

See issue: #6 and #7
I solve the issue #6 adding a "/" at the start of the path of every Link component, in this way gatsby is assured of internal link..
Instead for issue #7 i added the gatsby-transformer-javascript-frontmatter and in the blog (/en/ and /it/) index page i added:

export const frontmatter = {
  id:  '02',
  title: "pagina blog",
}

in thys way that page has not an empty id anymore.

[kalwalt]

I think i can merge it, issue #8 was related and it will not happens (i hope).