Add build script.

dsst/__main__.py

@@ -0,0 +1,10 @@
+import sys
+import os.path
+# Add current directory to python path
+path = os.path.realpath(os.path.abspath(__file__))
+sys.path.insert(0, os.path.dirname(path))
+
+from dsst_gtk3 import gtk_ui
+
+if __name__ == '__main__':
+    gtk_ui.main()