Since some time we have new stylesheets based on style parameters. For
compatibility reasons however old stylesheets were left in the project -
this commit removes them by reapplying the theme if old stylesheet is
detected.
At the very end of the startup process, check to see if we are using a
versioned directory from a previous version, or we are not versioned at
all but are using the system's default storage location (that is, not a
custom config path set on the command line, etc.). If so, offer to
migrate the old configration folders into new ones for the current
version.
