Automate profile setting

We can derive whether we are build a developement snapshot or
a stable version from the minor version number. So do that.
This way, we'll get the devel profile selected in the nightly
SDK, which will make the commit sha appear in the inspector,
which is useful to determine what nightly users are testing.

meson.build

@@ -787,9 +787,18 @@ gen_visibility_macros = find_program('build-aux/meson/gen-visibility-macros.py')
 
 gen_profile_conf = find_program('build-aux/meson/gen-profile-conf.py')
 
+profile = get_option('profile')
+if profile == 'auto'
+  if gtk_minor_version.is_even()
+    profile = 'default'
+  else
+    profile = 'devel'
+  endif
+endif
+
 profile_conf_h = declare_dependency(
   sources: custom_target('profile-conf',
-    command: [gen_profile_conf, meson.project_source_root(), get_option('profile')],
+    command: [gen_profile_conf, meson.project_source_root(), profile],
     capture: true,
     output: 'profile_conf.h',
     build_by_default: true,

meson_options.txt

@@ -124,14 +124,14 @@ option('man-pages',
 
 option('demo-profile',
        type: 'combo',
-       choices: [ 'default', 'devel' ],
-       value: 'default',
+       choices: [ 'auto', 'default', 'devel' ],
+       value: 'auto',
        deprecated: 'profile')
 
 option('profile',
        type: 'combo',
-       choices: [ 'default', 'devel' ],
-       value: 'default',
+       choices: [ 'auto', 'default', 'devel' ],
+       value: 'auto',
        description : 'Profile to use for demos')
 
 option('build-demos',