[Website] Update Home page

Need to update Home page according to TDD:

• Header (update text)
• Button to install Beam (change link)
• Beam Model (update place and text)
• Apache Beam Features (update place and text)
• Apache Beam Runs in These Environments (update place and text)
• They Tried It Out (update place and text)
• Twitter, Blog, and Event Cal Plug-ins (update place)
• Remove menu for the mobile version