Move to QWebEngineView

[raelgc]

Webkit is displaying too many issues with Slack JS, including the current blocker #594.

Let's check if using Chromium engine will improves the compatibility.

In Ubuntu, QWebEngineView is present in 18.04.

[raelgc]

Docs to read:

• Porting from Qt WebKit to Qt WebEngine
• Qt WebEngine Overview

[ArchangeGabriel]

Since the official app is just an electron embedding of the website (just as scudcloud is a QtWebKit one), it’s pretty sure that using Chromium would work. ;) So this would just be a Qt vs GTK embedding in the end (but with open sources, which is always better).