- Reduce platform specific code in ImageWriter class,
and move that to seperate classes.
- Use API calls to get current SSID on Windows and Linux instead
of launching command line utilities.
Tests if repository json files conform to the json schema.
If all resources (images/icons/website URLs) they mention actually
exists.
And can also test writing images and the FAT modification code.
Instead of using 'pi' as default, try to get the username of
the current user from the OS.
May not always work. (e.g. some Windows users may not have
setup a username themselves, but may be using a default user
created by the PC vendor).
Closes#497
