Reconstruct Reader: Set nonlinear transforms to identity

Bugfix for Reconstruct Reader (Reconstruct importer for TrakEM2)

Problem:
Reconstruct's nonlinear transforms are incompatible with TrakEM2. Previous versions of the translator, when encountering such transforms, ignore the nonlinear coefficients and display a warning message. Since images and traces are transformed independently, this often displaces the traces from the underlying image.

Fix:
The added code in this commit finds all nonlinearly transformed images. The image transform is set to identity and all corresponding contours are transformed to match the untransformed image.