Make zint backend required by default , and allow "--without-zint" only when flag set explicitly

[gwpl]

Hi!
I find zint backend crucial for good user experience for someone giving a try to glabels-3!
It provides so many barcodes types!

I found saidly that because it's optional by default, in many distributions users struggled with getting packaged with zint support compiled in - e.g. for some period of time in Ubuntu, now I struggle also in Archlinux. I am skilled, so despite inconvenience I can rebuild package on my own, but not all users are so eager, especially if they want to give a try to application -> it's high risk they may discard after seeing few barcode options available by default.

Therefore, I highly suggest to perform in following way to give a signal to package maintainers (of all distros) as same time :

• make zint required by default
• in case of lack of zint, make ./configure to display message "zint is highly recommended for good user experience, due to amount of barcodes it's provides. Although, it's possible to compile glabels-3 without zint. To do so, set '--without-all-what-zint-provides-I-am-sure' flag, but only if you are sure."

Ok, maybe I exaggerated a bit with name of flag ;) , but I hope I show my point.
I am just afraid that most package maintainers automatically compile thousands of packages never looking at them more carefully, so there is no chance they will add any optional dependency if it does not break fully automatic build and require human intervention.