popup.html: Remove unused code

Signed-off-by: Zhaofeng Li <hello@zhaofeng.li>
Split browser-specific code into separate files

Signed-off-by: Zhaofeng Li <hello@zhaofeng.li>
Bumping both extensions to 0.1.2

Signed-off-by: Zhaofeng Li <hello@zhaofeng.li>