Show hint message when entering lt or dr

This fixes the last issues mentioned in #9339.
Also init the IIR entry box when it's 1

GTK doesn't fire the signal of the slider we are listening to
(value-changed) when setting the slider to the same value as it was. And
since it defaults to 1 ...
This is relevant to bug #9339.
multi_name is a static string, fix test.

And initialize the string to empty. Cleaner and faster.
Move declaration where needed. Code clean-up.
New static routine to set the panel label.

Preparatory work for #9704.
New routine to update the panel header.

This routine update now the panel label. This is needed to be able to
display the proper multi-instance name when switching images.

Preparatory work for #9704.
When switching images make sure the header is updated.

This set the proper multi-name for the corresponding instance.

For #9704.
Make sure the duplicated module is saved in the history.

We do not want to save the new instance without having the previous
instance saved even when the first instance is not yet activated.

Fixes last issues reported in #9704.
rawspeed: experimental SONY ILCE-3000 (A3000) support)
adobe_coeff: experimental SONY ILCE-3000 (A3000) support
rawspeed: experimental SONY ILCE-7 (A7) support
adobe_coeff: experimental SONY ILCE-7 (A7) support
adobe_coeff: experimental SONY ILCE-7R (A7R) support
rawspeed: experimental SONY DSC-RX10 support
adobe_coeff: experimental SONY DSC-RX10 support
rawspeed: very experimental Panasonic DMC-GM1 support
adobe_coeff: experimental Panasonic DMC-GM1 support
rawspeed: experimental Nikon D610 support
adobe_coeff: experimental Nikon D610 support
adobe_coeff: updated Nikon D5300 support