Rework main page design

Rework main page design to be cleaner:

• Switch background image to 5.24
• Use better contrast and line heights on heading text
• Make heading image larger (at least 80% of the screen)
• Move "open up" section to the top, since it's the most descriptive for the project and easiest to read
• Add blue background to applications section, to differentiate it
• Make body text greyer to be easier on the eyes
• Fix some mobile layout issues