Add enabled/disabled flag

[mikeckennedy]

I think it would be nice to have an option to disable all events and page views. This way in dev and testing, if you're not wanting to trigger events but also don't want to change how you're using the API, just turn it off at app startup.

[mikeckennedy]

Fixed and published in https://github.com/mikeckennedy/umami-python/releases/tag/v0.2.20