autoupdate: integrate winsparkle

- Winsparkle is the windows port of Sparkle the framework used on OSX
to provide the autoupdate feature
- This commit add:
  - Winsparkle as a submodule
  - A check for update button in the configuration panel
  - All that is guarded by ENABLE_AUTOUPDATE to allow build without
  Winsparkle
  - Add a way for the user to enable/disable auto check for updates
  and to set the interval of these checks

Change-Id: Iea9cb0a31b60c8111f30a4f648d6f5e80b92abdc
Tuleap: #183
diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..fa045e1
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "winsparkle"]
+	path = winsparkle
+	url = git://github.com/vslavik/winsparkle.git