Log Message:
Update mate-desktop to 1.20.1:

MATE Desktop 1.20 supports HiDPI displays with dynamic detection and scaling.
HiDPI hints for Qt applications are also pushed to the environment to improve \ 
cross toolkit integration.
Toggling HiDPI modes triggers dynamic resize and scale, no log out/in required.

Full changelog:

Add gsettings for window scaling factor
drop additional checks for min GLib version
remove < gtk+-3.22 bits and bump required gtk+ version
schema: drop can-change-accels key, won’t work with GTK+3
WidthOfScreen and HeightOfScreen implementation
drop MateAboutDialog
mate-about: remove remains of libunique references
mate-about: switch to GtkAboutDialog
gtk 3.22: avoid deprecated gdk_screen_get_monitor functions:
avoid deprecated gdk_screen_get_width/height
mate-desktop-item: mate-about: avoid deprecated gtk_show_uri
mate-about: avoid deprecated gtk_show_uri
avoid deprecated gdk_screen_get_n_monitors
avoid deprecated gdk_screen_make_display_name
avoid deprecated gdk_screen_get_number
Correct little imprecision in man mate-about
Fix broken fallback cursor in mate-colorsel.c
mate-colorsel: don’t use deprecated GTK_STOCK_COLOR_PICKER
Add Global Menu support
Translations update