Build clamshell and blip in runservers

A set of changes to adapt `runservers` to new webpack workflow for Blip and Clamshell.

Basically we build both apps with a "local" config, then launch their static servers.

Since the build script is quite verbose, I redirect its output to `/dev/null`.

Since the build can take some time, I added to ability to set `export SKIP_BUILD=true` before running the `source tools/runservers`. But this is only "if you know what you are doing", i.e. by default it will always build.

@cheddar @kentquirk let me know what you think?

Thanks!

See https://github.com/tidepool-org/tools/issues/18
That does.  It does mean that I'm going to have to change around my workflow for when I muck with blip (regularly enough, fwiw).  That's fine though, especially now that I'm aware of it.

Btw, when you started the discussion, you said, 

> So for the runservers script, I'd like to just fire node develop.js for Blip and Clamshell, which quickly starts a static server.

Which is why I thought you were keeping the develop.js behavior and just building up the config object.