Popup Video(WebExtension) nga Ett Chung

Pop-up Youtube/Twitch video to standalone window.
========================
NOTE:
1. PLEASE report issue here: https://github.com/ettoolong/PopupVideo/issues
Don't left any bug report or function requirement at review comment, Thanks.
========================
This add-on is porting from Popup Video(https://cup.aihedy.com/zh-TW/firefox/addon/popup-video/)
Because of the WebExtension API limitations, I removed the below functions:
2. Set pop-up window resizable (all windows are resizable)
3. Set pop-up window always top

Usage:
1. Right click on Yotube video link, click [Popup video window] to popup video window.

2. Mouse over Youtube thumbnail, click the [Popup video window] icon to popup video window.

3. Open pop-up window by other add-on,
for example: Foxy Gestures(https://cup.aihedy.com/zh-TW/firefox/addon/foxy-gestures/)
browser.runtime.sendMessage('PopupVideoWebExt@ettoolong',
{
action: 'launchVideo',
url: data.element.linkHref
}).then();