Enable active project flag after importing an Eagle project

When active project flag is disabled, the application buttons are
disabled in the main launcher window. It usually happens when 'kicad'
runs without any project preloaded.

kicad/import_project.cpp

@@ -214,4 +214,5 @@ void KICAD_MANAGER_FRAME::OnImportEagleFiles( wxCommandEvent& event )
     }
 
     ReCreateTreePrj();
+    m_active_project = true;
 }