Allow disabling default global tags

[vfaronov]

Geany ships with default global tags for a few languages.

Personally, I find that the Python tags are more of a nuisance. Python is a heavily namespaced language: just because there is a function named check_value somewhere in the Python standard library, doesn’t mean that check_value should be suggested as a completion everywhere in every Python file I edit.

So, I want to disable the default global tags for Python. But the only way I see of doing that is by removing the $PREFIX/share/geany/std.py.tags file. I think this is not very nice, because this should be a user-level, not system-level change.

There is the -n / --no-ctags runtime option, but it disables all global tags, whereas I only want to disable some.

Perhaps, ideally, if the user has a customized std.py.tags on their private config path, that should override the system-wide std.py.tags rather than extend it?