added a page for apps development with a basic first description

of possible app types, defined in the info.xml

developer_manual/apps.rst

@@ -0,0 +1,19 @@
+Apps Development
+================
+
+Supported App Types
+-------------------
+
+ownCloud allows to specify three kind of "types" in the info.xml of a app. The
+type doesn't have to be specified if the app doesn't match any of them.
+
+Currently supported "types":
+
+**filesystem**
+apps which provides filesystem functionality (e.g. files sharing app)
+
+**authentication**
+apps which provided authentication backends
+
+**logging**
+apps which implement a logging system