Support `--only` and `--except` options for bin/integration

Adds command-line flags for `bin/integration`:

* `--only` will limit the integrations to those given
* `--except` will exclude any given integrations
* `--list` will output the list of integrations during the build

This is useful for producing custom builds.

Example usage:

    bin/integration --only uservoice optimizely
    bin/integration --except pingdom quantcast rollbar --list