Improve action hierarchy for header and hero sections

[gtsiolis]

Problem

1. We're missing a CTA button on the header navigation.
2. We want to add a link to the GitHub repository, per https://github.com/gitpod-io/website/pull/862#issuecomment-739506303.

Proposal

1. Replace the top right sign in button with a primary action button.
2. Introduce a secondary button next to the primary button the body.
3. Use the new secondary button to link to GitHub.

To make the proposal more clear, here're some mockups.

BEFORE	AFTER

[chrifro]

I like the idea of having a CTA button in the navigation bar. When we first created the website the thought was:

• have a login button if you already have an account
• have a get startedbutton if you're new to Gitpod

Unfortunately we'd couldn't get that implemented. What do you think about this? Any idea how to do that? Maybe by using cookies?

Theget started button could link to https://www.gitpod.io/#get-started