Add functions for updating adjustment settings

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Add function to config-ini that gets multiple sections with the same name

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Rewrite gamma-dummy to use gamma-common and update redshift.c to use gamma-common.
When compiling, disable all other methods until they too have been rewritten to
use gamma-common.

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Rewrite gamma-randr to use gamma-common

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Rewrite gamma-vidmode to use gamma-common

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Rewrite gramma-drm to use gamma-common

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Rewrite gamma-w32gdi to use gamma-common

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Remove the old colorramp_fill

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Add preserve-calibrations (-P) option

Signed-off-by: Mattias Andrée <maandree@operamail.com>