modules: add configurable module-tree grouping (category/language/both)

[LAfricain]

• new setting modules/grouping in settings.conf (0/1/2)
• main_load_module_tree_flat() and main_load_module_tree_by_language() in main/sidebar.cc, dispatched from main_load_module_tree()
• new combobox in Preferences > Modules Misc (prefs.glade + prefs.gtkbuilder)
• right-click on a category/language folder also offers the 3 modes

Addresses part of the display-customization ideas raised in #1130.

[LAfricain]

I realized too late that I created this branch from another branch that was still in progress! Two files were modified but aren't needed here sword_main.cc and sword_main.hh. I'm currently figuring out how to fix this.

I often run into this problem when creating a new branch that branches off from a branch other than the upstream branch.

[LAfricain]

Sword repository is down. Windows build fails for this reason.

[karlkleinpaste]

Being a paranoid soul, I tried re-triggering the failing Windows builds, just because it seemed a good idea.
It didn't work, due to a dnf problem. I am ... confused.

[LAfricain]

This looks unrelated to this PR — the failure happens in the Docker setup step (dnf -y update --refresh && dnf install ...), before any Xiphos source is even compiled. Our changes here only touch .c/.cc/.h/.glade/.gtkbuilder files.

Per INSTALL.md, the Windows cross-build requires Fedora 30 (since Fedora 31+ dropped webkitgtk). Fedora 30 is long EOL, and its repos have since been pulled from the standard mirrorlist and moved to archives.fedoraproject.org. A plain dnf update --refresh against an EOL release will fail once that happens — this is a common, recurring issue for Docker images pinned to old Fedora releases, not something caused by this patch.

This is almost certainly transient. Re-run the job first, in case it's a transient mirror hiccup.

[LAfricain]

Now sword is down again. I wanted to suggest that we point to the sword mirror on GitHub to download the archive—it’s more stable. Lately, there have been recurring issues with the servers going down. That’s actually what worries me more broadly. I mentioned it on the mailing list, but I didn’t get any response.

[karlkleinpaste]

That's very nice. A fine enhancement.