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
Ah my bad, I meant "fire node server.js" :)

If you are working on Blip code, I would suggest not running it via `runservers` (i.e. commenting out the correct line), and using `source config/local.sh; npm start` in a dedicated terminal in the Blip directory (`local.sh` can be just export statements in `tp_blip`).

That's why in #18 I raised the question of should we have front-end apps in `runservers` at all. But that can be for some other time...