Add mailing list signup to landing page

[exitonoff]

Addresses https://github.com/SharedStake/SharedStake-ui/issues/65.

Texts and placeholder text can be changed. I stripped down some initial styles which were included in the html provided.

I also noticed that there's prolly typo in Mailchimp, since the url is https://**sharestake**.us1.list-manage.com as it should be sharedstake. The return from the signup leads to nowhere (sharestake.org).

Please comment on the styles if you have any suggestions:

[exitonoff]

Updated the link and title.

[sharedStake-main]

Approved @exitonoff