This turns `paginationInProgress` field of `TimelineModel` into a `Q_PROPERTY`, so the Ui can bind to it.
For the moment, I'm showing the same spinner as we do during initial sync. It's not ideal, on the count of being giant and in the middle but it's better than nothing. We can make it more subtle later.

I mean, we're both GPL so... :P

Also make hidden entries not consume space in Menus with some qml
styles.

fixes #124

Can't do it for QtWidgets code. We need to fully transition, before we
can fully switch over probably.

It made some messages unreadabe. We loose proper highlight colors, but
we will have to do for now, until I can figure out, why the TextArea
doesn't work.