Add logic to turn off network requests when Scope dismounts

[jpellizzari]

Needed for https://github.com/weaveworks/service-ui/pull/184.

When navigating to another page in Weave Cloud, Scope will be unmounted by react-router. This change will turn off topology polling and websocket connections when Scope dismounts.

[jpellizzari]

@davkal If you could review when you get a chance. I pushed up a commit on service-ui that does a LocalModuleProxy to a local Scope repo. You can test this change along with the scope as a component PR by doing:

SCOPE_PATH=/path/to/scope PROXY_SCOPE_COMPONENT=true npm start

in the service-ui repo.

[jpellizzari]

Added some extra files to support doing partial imports, ie:
import reducer from 'weave-scope/reducer'

I originally attempted to avoid polluting the app/scripts directory with more files using a bash script when building the npm package...

#! /bin/bash
split -l 1 app/scripts/index.js ../tmp/module__
for file in `ls ../tmp/module__*`; do
  contents=$(cat $file)
  module_name=$(echo $contents | grep -oE 'exports\.(.*?\s)' | sed 's/exports\.//')
  filename="build-pkg/$(echo "$module_name.js" | sed 's/ //')"
  rm $file
  touch "$filename"
  echo $contents > "$filename"
done

...but that will not work with LocalModuleProxy.

[davkal]

Small code nits. Otherwise LGTM