Credit: Jaroslav Ryník

I can't get the mobile site to display correctly; the position of the
contents moves around depending on the widget's position on the board.

Switched back to the desktop site because it's not worth spending days
on this.

Credit: Jaroslav Ryník

(widgets' size and position weren't necessarily calculated based on
their current screen, but on the entire desktop geometry)

This also fixes the skewing observed during podcast recording

Adds Pixabay image search, to replace the defunct Google search

also added a function to get slightly larger images (though the Pixabay
API doesn't give width and hight info about these, so it's not currently
used)

- Fixed display
- Fixed/added support for pages
- Added image title generation, so it can be e.g added to OpenBoard
library

removed references to youtube from videoPicker widget (youtube embedding doesn't work, won't be fixed soon)

e.g 1.3.0-rc.1, or 1.3.0

Also, changed version number to 1.3.0-rc1

Search basically works; but just one page of elements are retrieved.
Metadata is assigned ok.
To do: paginate search results; correct display; and later, add filters

- Display a meaningful error message to the user when adding or trying
to play a video
- Make sure the video placeholder is visible even after switching pages