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.

Improve scrolling in timeline view

Fixes #180

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

Sometimes thumbnails still have the wrong dimensions, as they are scaled
to fit inside a rectange of the reported size in the image. Not sure,
who is wrong there, the media repo or we.

Decrypt sidebar setting added to user settings

fixes #172

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

fixes #170

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