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.
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
adobe_coeff: updated Olympus E-M1 support