Prevent opening text files

Opening a text file would overwrite the current draft, so for now we'll
disable this.

data/writeas-gtk.desktop

@@ -2,10 +2,10 @@
 Type=Application
 Name=Write.as
 Comment=Publish a thought in seconds.
-Exec=writeas-gtk %f
+Exec=writeas-gtk
 Icon=write-as
 Terminal=false
-MimeType=text/plain;
+MimeType=
 Categories=GTK;Office;Publishing;
 Keywords=blog;text;editor;publish;
 StartupNotify=true

src/application.vala

@@ -32,11 +32,6 @@ public class WriteAs.Application : Gtk.Application {
 
     public override void open(File[] files, string hint) {
         activate(); // ensure we have a window open.
-        try {
-            (get_windows().data as MainWindow).open_file(files[0]);
-        } catch (Error e) {
-            error(e.message);
-        }
     }
 
     public static int main(string[] args) {