Added session downloader for chrome extension

[kirankunigiri]

• The session list page now has a button to download sessions as .json files for use with rrweb-player
• Improved styling for the delete and download buttons

I got the idea for this because I wanted to use the chrome extension to download a recording of my project and use it in my own landing page, since the file size is much smaller than a normal video. This allows users to export their recordings to JSON file with the chrome extension and use it with rrweb-player in their projects.