New landing page as discussed in #125

Just noticed this also includes the changes I did in header-footer ([in PR#45](https://github.com/asm-helpful/helpful-web/pull/45/files)). Helpful is the first time I'm working with PR's so please forgive me :-)

This is probably because the styles are dependent on some changes I did in the styles in the header-footer branche (which I merged locally into master, from where I branched my new landing-page branch).

The landing page updates are only in commits 40af528 & 5268311. Sorry about the hassle :-)