Use current default build for comparison in version discrepancy table

[xKevin04]

This feature is still a work in progress I think (can you even navigate to it?), but the version discrepancy table should ignore builds that are on a branch or not available via Galaxy anymore to determine a discrepancy with the offline installers.

There may be a case to be made for beta channel versions as you can install them with Galaxy, but I think that would bloat the table unnecessarily. The version that's installed by default should be considered stable and is therefore relevant for pretty much everyone, I doubt a lot of users check beta channels and use them.

Two examples are Songs of Conquest, which has it's newest (test) version only available as part of a beta channel, and Volgarr the Viking II, where the newest version has been pulled and we have no choice but to install the older one now.

[Yepoleb]

I wasn't that aware of branches when I wrote the feature, but it definitely makes sense to implement. Thanks for the suggestion!