Feature/daef 418 About page, available from the system menu

[tomislavhoracek]

This PR introduces about page window from system menu.

[DominikGuzei]

@tomothespian great work! The only thing that bothers me is that it takes a few seconds before the about window appears on screen … do you think there is any chance to make it faster?

[nikolaglumac]

@DominikGuzei: @tomothespian and I have tried to find a way to speed it up and failed :(
The only possible way to speed it up would be to pre-generate about page in pure html. That way it would be displayed instantaneously BUT this approach has 2 pitfalls: we need theming and translations support.
In the end I don't think our About page is much slower (or at all slower) than the one from Slack ;)

[DominikGuzei]

Ok thanks for the report 👍 you're right, this seems to be a problem with electron / rendering speed of the web app. It's not critical since the about page is not viewed regularly 😉

[DominikGuzei]

Merging when CI is done

[darko-mijic]

Let's not merge it until we update the list of people.