Support the TARGETS selection

The TARGETS "selection" (X11 nomenclature) is used to list the available
formats for selection conversion.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Make sure cantera-term.desktop is installed

A cantera-term.desktop was created long ago, but the command in Makefile.am for
installing it disapparead.  This commit reinstates it.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>