Extract DConf dependencies into a separate role

Both GDM and GNOME uses DConf to manage its own configuration. Extract
the common dependencies into a separate role called "dconf".
DConf provides:
  - creating empty directories for configuration
  - handler to apply configuration when configuration has changed

roles/dconf/tasks/main.yml

@@ -0,0 +1,6 @@
+---
+- name: Creating DConf database directory
+  file: path=/etc/dconf/db state=directory mode=0755 recurse=yes
+
+- name: Creating DConf profile directory
+  file: path=/etc/dconf/profile state=directory mode=0755 recurse=yes

roles/gdm/meta/main.yml

@@ -0,0 +1,3 @@
+---
+dependencies:
+  - { role: dconf }

roles/gnome/meta/main.yml

@@ -1,5 +1,6 @@
 ---
 dependencies:
+  - { role: dconf }
   - { role: x }
   - { role: gdm }
   - { role: networkmanager }