JS: include the context this file reads through

EditContext.ui.cpp reaches into doc->app to ask the layer factories
whether a process has an external UI, but never included the header that
defines GUIApplicationContext -- it arrived transitively, and no longer
does. Building master gives:

  error: member access into incomplete type
         'const score::GUIApplicationContext'

A precompiled header hides it wherever one is used, which is why it
survives some configurations and not others.

Author: jcelerier

src/plugins/score-plugin-js/JS/Qml/EditContext.ui.cpp

@@ -6,6 +6,7 @@
 
 #include <JS/Qml/EditContext.hpp>
 
+#include <score/application/GUIApplicationContext.hpp>
 #include <score/tools/std/StringHash.hpp>
 #include <score/widgets/DoubleSlider.hpp>