Rearrange the order of sections on the main subpage

[rw1nkler]

The webpage should be arranged in the following manner:

1. call to action text
2. news / updates / what has changed recently
3. pretty pictures / diagrams / etc
4. More detailed background information

Additional changes in the layout:

• Sections 1 and 2 should appear "above the fold" at normal computer resolutions.
• There should be two calls to actions in the first section:
  • "Getting started" -- A call to action around getting started as a user of the toolchain.
  • "Help contribute" -- A call to action around helping the SymbiFlow project.
• The information about development boards should be placed above (or maybe even behind) the "getting started" call to action.