General way to handle configuration for plugins

[ward]

Twitter and strava plugins require API access information. This should be somehow defined in the plugin list but requires some rethinking of that part of the configuration.

[ward]

Retake-name could also use specific configuration: how often to check to retake the name.

[ward]

Would also want some standard functions to check for the (required) presence of these configuration values.

Q: If not present, stop loading the bot entirely or just abandon loading that specific plugin? If the latter, is this something that can just be halted within the plugin?

[ward]

Concerns this part

let stravaconfig = config.get('bot.strava');
for (let key in stravaconfig) {
  if (stravaconfig[key] === null || stravaconfig[key] === undefined) {
    throw new Error('Tried to load strava plugin, but credentials are not present: ' + JSON.stringify(stravaconfig));
  }
}

[ward]

Along the lines of what a plugin should then put near the start of its script:

let account = plugin.requires('account');
let time = plugin.accepts('time', 'some default value');

If a requires() call fails (turns out there is no such information), then loading the script should halt, an error should be printed, but the bot should carry on without that plugin.