Refactor web and chome backends

[akshaybadola]

chrome and eww functions are in ref-man-chrome.el ref-man-web.el and some old functions in ref-man-core.el also.

• chrome backend should be part of the web backend and functionalities like history, bookmarks and shit should be universal eww functions.
• Bunch of them are in chrome and some in eww. Chrome should be optionally set and all eww features like histories bookmarks should be together.