Disabling the new version check at compile time

[kini]

It would be nice to have a compile-time configuration option to disable the behavior where YACReader connects to github to look for new versions and pops up a dialog box telling the user to go to the website to download the new version.

This would be useful for packaging YACReader for Linux distributions, since usually when a user has installed a program from their distro's central package repository, they will not want to download and install a new version directly from the program's website. Instead, they would usually prefer to wait for the central package repository to get the updated version.