When running algorithms through the toolbox, which have dynamic
numeric parameters, add a data defined property override button
next to the widget so that users can set the overrides for these
parameters.
Previously this was available only in the backend, but not
exposed anywhere in the GUI.
Note that currently no algorithms support dynamic parameters,
so don't expect to see this everywhere. It's also only available
in toolbox/batch processing modes, not in models.
901dae1110