Support only render chosen file

[Kyson]

It is too slow render all diff files content, why not render the chosen file by click on file list item, and its more clear for users

[rtfpessoa]

I went ahead and since this was already talked before I did a PoC.

• Check out branch support-files-lazy-loading
• Run yarn
• Run yarn build
• Open docs/demo.html

Let me know what you think and suggestions about it.