improve landing page

[veitu]

• [ ] “Pledge. Measure. Solve.” slogan should always be centred, independent of the zoom level
• [ ] The following sentence and the two buttons (subscribe, check out demo) should always be readable/visible under the photo on the main page (now the user has to scroll down) “Pledge4Future is a project to help you and your working group to measure and reduce your work-related CO2e-footprint. “It helps you and everyone else to contribute protecting our climate and life on Earth.”
• [ ] Line break after “Pledge4Future is a project to help you and your working group to measure and reduce your work-related CO2e-footprint.” → Second line: “It helps you and everyone else to contribute protecting our climate and life on Earth.”