Create an About page
Right now the About button does nothing. It should show:
- a brief description of what Parity Signer is with security advices (no network)
- talk about the rust code audit
- mention that there is no data gathering at all
- a link to the wiki
- a link to github
- "developped" by Parity Technologies
- the app version
@Tbaut to write it @fckt to add it :)