Use a print servlet listening on port 80 in examples

This changes mostly three things with regard to our use of the mapfish print servlet:

* In the examples we use a print servlet listening on port 80 so people pbehind more restriictive firewalls have a chance of testing the functionality
* for consistency, the URL has also been changed in the tests, where we now use the same servlet
* while I was at it, I refactored the print tests to use the variable `printCapabilities` by including a shared JS-file instead of the copy-pasted variant before.

Thanks for any review.

fixes #306
cc @chrismayer, @weskamm