Updated dev commands

Moved commands from a directory to a single script.  I think this is
good because:

  - It's how most other nice command-line programs do things (git,
    fig, docker, etc).
  - Easier access to documentation.  Run "dev" for a list of commands
    and "dev help <command>" for help on a single command
  - Can name commands without worrying about conflicts.  For example
    "dev bash" instead of having to use "amara-bash"

Added section in fig.yml to run a bash prompt.

Moved show-server-local-settings into the bin/ directory.  It doesn't
really fit with the rest of the dev commands, so I kept it separate
from them.
Javascript test update

Added a jstest dev command.

Fixed our karma conf to work with newer versions.

This goes along with another change that makes the amara/jstest image.
It runs the tests using PhantomJS (AKA headless chrome).