VisdomLogger username and password configration

[ricardofbarros]

At the moment it is not possible to configure the Visdom client with a username & password. Making it impossible to use this repo when you have a visdom server with auth enabled.

I'll gladly submit a PR with this feature if you think this is something you would accept.

The implementation would be passing username and password from the logger classes until it gets to visdom.Visdom, like:

self._viz = visdom.Visdom(
    server="http://" + server,
    port=port,
    username=user,
    password=pass
)

[ricardofbarros]

cc/ @szagoruyko