Registration: in estimate_affine check that selected points are not outside of the data volume when in grid mode

[ieivanov]

In grid mode, it's possible to incorrectly mark a point in phase with the fluorescence points layer selected. This will result in improper registration. We can have a check that the coordinates of the point are within the data volume. It may also help to display the message (e.g. "select a point in the fluorescence channel") for every click.