Rework admin and stream servers

* Remove listening code from Master.Admin.Router and Slave.Server
* Add listening strategies into different modes in Core
* Rewrite Slave.Server to newer express style
Reorganize assets for the admin UI

* Move from connect-assets to mincer for asset compilation
* Move assets into master/admin/assets
* Pass the express app path into the admin to allow support for mounting at
  /admin in Standalone mode