don't change the default here

this code needs to fulfil three different cases:

- no mlite available, THEME_NAME not hardcoded: typical desktop case, to support the old nokia theme (hence blanco is correct)
- mlite available, theme given: self explanatory
- no mlite available, THEME_NAME hardcoded: for desktop cases where you want a theme other than blanco (e.g. we use this inside Jolla to prototype with silica on desktop)