Ability to enable collector & evaluator independently

The native Cube server can only be started as a collector or an
evaluator. Cube express allows you to enable them independently so you
can turn both on if you'd like.

The behavior is controlled by ENV vars. You can turn the features on
with:

    ENABLE_COLLECTOR=1
    ENABLE_COLLECTOR=1
Add travis config
Enable server features in Travis
Simplify makefile and make tests pass
Merge branch 'travis'