Issue-65 Enable Stream on multisite / network installs

Hey Guys,

This is not ready to be merged yet but I wanted to get some feedback from testing and suggestions.  I've added a `blog_id` column to the database table and updated the queries and logging classes to enable multisite support.

The plugin can be activated on any combination of network sites or network activated from the network admin menu.    When activated network wide, the stream admin screen is added to the network administration menu and activity from the entire network is displayed.  I've also added a blog filter to the network stream.

I'm adding a network options page to enable network wide settings that can be overridden on a site by site basis if needed along with an option to hide the stream page from the sites so that only the super administrator has access.

Is there any other network features we should include?

cc @fjarrett @shadyvb

Fixes #65