Read title from settings, when the setting exists

Reading the title from the settings of the active profile was not working.
This adds the needed machinery to honor the settings or the command line,
whichever has more precedence.
Remove FIXME about window borders, it was a VTE bug

Now that dwt is using VTE 2.91 this issue does not happen anymore, so it
seems reasonable to think it was caused by a bug in VTE 2.90 and the FIXME
can be removed.