Re-design top page for better impression

[rozq]

• [x] add showcase pictures #30
• [x] more concise introduction
• [x] search box #11

[rozq]

re-allocated the words of index and about made the title align center

[rozq]

click in the search box, it will show adv search option

[rozq]

click the adv search button, the mega search area will collapse. add a svg close button

[rozq]

Done!