One surprise was that the main usecase of pasting is one where the user
activates another app to go and copy data in order to come back to paste
it.
And the Qt clipboard didn't manage to get any notification of clipboard
changes. Even copying data on becoming active had no effect.
So now I just show the paste optimistically when the user comes back
from another screen, assuming the main reason for that was to copy.
This makes available a clipboard helper component in QML.
Based on filters we then can make the 'paste' button visible and
only allow pasting stuff that is remotely useful.
This then also adds a 'paste' button to the transaction-building
module, the 'destination' screen.
tomFlowee