cmake: use LibFindMacros
Silence a CMake warning
cmake: fix error in FindLibsecret.cmake
Fix a small leak found by Coverity
Tiny code change to fix show_icons_in_paint_c.pl

... by removing some intraproject dependencies from the code.
OSX: fix DPI detection
fix possible use of uninitialized value in previous commit
Switch to GTK3 in cmake
Import osm-gps-map-1.0.2

Previous versions does not compile with GTK3
Cleanup CMake system now that GTK uses pkg-config
Respect REQUIRED when looking for GTK3 components
Load darktable.css instead of dakrtable.gtkrc

This is just a sample .css file with a dark background color to see if
loading worked.
Temporarily enable deprecated GTK/GDK symbols
Add -Wno-error=deprecated-declarations to FLAGS
GTK3: gtk_paint_box format has changed

Relevant Coccinelle patch:
@@
expression STYLE, W, STATE, ST, WG, DEL, STR, X, Y, WD, HT;
@@
gtk_paint_box(
STYLE,
-W,
+gdk_cairo_create(W),
STATE,
ST,
-DEL,
WG,
STR,
X,
Y,
WD,
HT)
GTK3: size_request is now get_preferred_(width,height)
GTK3: expose_event is now draw, second param is different
GTK3: GtkObject is gone

GtkObject has been removed in GTK+ 3. Its remaining functionality, the ::destroy signal, has been moved to GtkWidget. If you have non-widget classes that are directly derived from GtkObject, you have to make them derive from GInitiallyUnowned (or, if you don't need the floating functionality, GObject). If you have widgets that override the destroy class handler, you have to adjust your class_init function, since destroy is now a member of GtkWidgetClass.

See https://developer.gnome.org/gtk3/3.10/ch24s02.html#id-1.6.3.4.15
GTK3: gdk_devices_list() is gone
GTK3: gdk_device_get_core_pointer() is gone