Create fake app info for unknown windows

[lenemter]

Fixes #310 (Basecamp app)
Fixes #423
Fixes #428

Some windows run in portable mode (for example AppImages) and they do not provide any .desktop files by default. Right now Dock doesn't even show these windows. This branch constructs fake app info for them and always shows them.

I couldn't find a way to trick GLib.DesktopAppInfo into using fake data, so I created a wrapper for it.

Before

After

[teamcons]

Reiterating the need for a fallback, to avoid people thinking (legitimately) the dock is broken
And to cover cases such as the above mentioned:
-Appimages
-Half baked APT apps
-Portable binaries
-When developing, testing prototypes

It could be a star or a grey question mark

[tintou]

Doesn't something like this work:

var keyfile = new GLib.KeyFile ();
keyfile.set_string (GLib.KeyFileDesktop.GROUP, GLib.KeyFileDesktop.KEY_TYPE, GLib.KeyFileDesktop.TYPE_APPLICATION);
var empty_appdata = new GLib.DesktopAppInfo.from_keyfile (keyfile);

[lenemter]

@tintou You can't set fake id with this and using window title instead is too unreliable since 'Unknown window 1' can have 'Unknown window 2' as a modal dialog for example, but they'll be shown as separate icons.