Rework Windows launchers:

- Use SDL2 message boxes instead of Winforms.
- Use a proper project instead of compiling a single file.
- Use assembly attributes instead of modifying strings in the source code.
- Remove generic OpenRA.exe launcher.
- Replace MakeLAA.exe with a python script.

OpenRA.WindowsLauncher/App.config

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<configuration>
+  <runtime>
+    <loadFromRemoteSources enabled="true" />
+  </runtime>
+</configuration>