Make initial loader opaque to hide app loading

[mczepiel]

I also brought the loader widget higher up along the z axis so it's
visible if necessary,but it doesn't look quite right as it doesn't have
the same dimensions as the loader that follows it (very quickly) due
to the text and some extra padding.

I don't want to lose the bootstrapping loader but wouldn't mind it
being different enough that the jump to the actual longer loader is
less jarring.

[mczepiel]

@simurai, please look this over; I don't think it looks great but the mechanics are in place.

• The bootstrapping widget is 100px tall while the regular one is 150px AFAICT
• The bootstrapping widget is off-center vertically from the regular one due to content difference, but when moving from one to the next, it's not pretty
• We don't transition out of the opaque loading screen, but I'm happy we don't transition into it (it was ugly)
• There's a lot of padding between the regular loader and the progress text

[simurai]

We could make both loaders have the same position, but there would still be a flash when they switch, right? Plus the colors wouldn't match.

Ok, sure. Let's change the first "bootstrap" loader to something else.

• Less padding (Already done in Firefly)

[simurai]

Added a mini version:

There is quite a long break till the second loader appears. Not sure, maybe it's just for me locally since I also have that error later?