Loads all plugins.

@param program Program or Plain object.
@param callback Termination.
function (program, callback) {
    var config = configHelpers.getConfig();
    config.plugins = config.plugins || {};
    var loadPlugin = function (pluginName, cb) {
      pluginHelpers.loadPlugin(pluginName, program, cb);
    };

    Object.keys(config.plugins).forEach(loadPlugin);
    nodeHelpers.invoke(callback);
  }