Added remote.name.annex-web-options config

Added remote.name.annex-web-options config

Which is a per-remote version of the annex.web-options config.

Had to plumb RemoteGitConfig through to getUrlOptions. In cases where a
special remote does not use curl, there was no need to do that and I used
Nothing instead.

In the case of the addurl and importfeed commands, it seemed best to say
that running these commands is not using the web special remote per se,
so the config is not used for those commands.