Show tooltip build button dependencies

It was confusing (for me at least) to open a project in GNOME-Builder and see that I couldn't build it right away, since the animation for downloading dependencies is quite subtle.

This PR sets the tooltip contents of insensitive build and run actions to message indicating that the build pipeline is currently being set up and thus the project cannot be built or run.

It also fixes a bug which causes tooltips not to show.

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