App: standard path handling

* distinguish between temp and cache location
* document's transident directory is created in the cache location
* add functions to access temp and cache location via Python

src/Gui/DlgEditFileIncludePropertyExternal.cpp

@@ -65,7 +65,7 @@ int DlgEditFileIncludePropertyExternal::Do(void)
     QFileInfo file = QString::fromUtf8(Prop.getValue());
     assert(file.exists());
 
-    QDir tmp = QString::fromUtf8(App::Application::getTempPath().c_str());
+    QDir tmp = QString::fromUtf8(App::Application::getUserCachePath().c_str());
     QString TempFile = tmp.absoluteFilePath(file.fileName());
     QFile::remove(TempFile);