Split out the UI component from the server component

[shankari]

They are really not related, except that we check both of them out on the e-mission server.
Combining them:

• makes the server repository unnecessarily big,
• requires the node/npm/bower stack on the server, which is not needed otherwise, and
• causes a ton of diffs as libraries are updated beyond the checked-in ones.

We should split out the UI code and make it available as a submodule instead - to be used only on production servers, if people want. The main e-mission server repository should still have a web page served by default, but it should be a simple static page with no dependencies.

[shankari]

This should make the docker script (#594) much easier...