TGMMImporter: be more verbose.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
State that we want Doubles and not Floats in display parameters.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Fix a bug in TGMM importer causing the wrong transform to be used.

We were using the transform at timepoint t when we should have used the
transform at timepoint frame[t].
Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>