Pass turnilo context to routers

[adrianmroz-allegro]

Right now, we're passing explicitly some settings (via SettingsManager) to each router creator (like https://github.com/allegro/turnilo/blob/master/src/server/routes/mkurl/mkurl.ts#L40)

Ideas:

• Full blown express middleware
  • Pros: industry standard
  • Cons: we have very little route code, could be overkill
• Attach SettingsManager (or some composed Context object) to Request
  • Pros: Simpler, better expresses immutable nature of settings
  • Cons: Still need to attach something to each request and pass request object in helper methods.