Add gulp
Create some basic gulp tasks

A task to generate minified/concatted CSS/JS, and a task to build the
server binary.
Add gulp go-build task

Compiling code via gulp automates the issue of GOPATH setting. This will
tie in with some gpm-related tasks that are coming in a future commit.
Refactor GOPATH calculation in gulpfile

Moving this into a function feels cleaner than a global, since the
calculation may be used by many tasks.
Always build the same binary name
Use gulp default task to build all
Add gulp serve task

Although environment variables are the best configuration method for
production, they are inconvenient in development because they are sticky
(ie they persist through your shell) and they are invisible (you can't
tell they're active unless you echo them). I much prefer setting those
variables with flags so I can see them on every command line. This task
lets us translate flags into env variables easily.
Add basic gulp test task

We'll need to spruce this up so that it can test the backends too. And
maybe hard code paths instead of using ./...?