getConfig got a remote-specific config, and this confusing name caused it
to be used a couple of places that only were interested in global configs.
Rename to getRemoteConfig and make getConfig only get global configs.
There are no behavior changes here, but remote.<name>.annex-web-options
never actually worked (and per-remote web options is a very unlikely to be
useful case so I didn't make it work), so fix the documentation for it.
Locking is used, so that, if there are multiple git-annex processes
using a remote concurrently, the stop hook is only run by the last
process that uses it.
