Date::Pcalc -> Date::Calc

Date::Calc is nowadays pure perl (but may use Date::Calc::XS if available), so
there's no need anymore to use Date::Pcalc (which does not work since
perl 5.16 anyway).
first steps for travis testing

* don't prereq "difficult" modules like Image::Magick or X11::Protocol
* use "test-no-cgi" target
added .travis.yml
added Geo::Proj4 to list of uninstallable dependencies
travis build: removed 5.8 because of DBD::XBase issues
travis: added GD and dependencies to the list of uninstallable dependencies