Move mimetype definitions to plugin specs

- Avoids the hassle of QRC files and manually registering mime types
- Avoids performance regressions because of mime types that are
  registered after mime database has been used
- Makes it technically possible to detect that a disabled plugin could
  handle a mime type if it was enabled

Change-Id: I373008b1b56e9c6b4853055f20b3eeb112a6eff9
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/pythoneditor/pythoneditor.qbs

@@ -17,7 +17,6 @@ QtcPlugin {
             "pythoneditor.cpp", "pythoneditor.h",
             "pythoneditorconstants.h",
             "pythoneditorplugin.cpp", "pythoneditorplugin.h",
-            "pythoneditorplugin.qrc",
             "pythonhighlighter.h", "pythonhighlighter.cpp",
             "pythonindenter.cpp", "pythonindenter.h",
             "pythonformattoken.h",