#1 Add option to override query at startup

[Andreas Stemmer]

I wanted DesktopAid to restore the last session without having to
confirm the default session each startup. This little patch adds a
customizable option "dta-always-use-default" which overrides the
query at startup if set.
Please note that this is my very first attempt of writing Lisp code,
but it seems to work and could be of help for others perhaps.

[Andreas Stemmer]