Added docker runtime and some env configurations

[Stopka]

Hi, I made it runnable as a standalone app in docker.

For this reason I also made few features configurable by environment variables:

• BOSH_URL if set it hides the bosh input in login form and uses it's value
• SERVICE_WORKER if true the service worker is registered, otherwise it is unregistered
• SECURE_HOSTNAME you can define other hostname as secure, defaults to localhost (usefull if you use proxy in local environment with domains in form of example.localhost)
• ENVIRONMENT_SECURITY_MODE you can set if the app refuses to start as before (strict), or it should just shows a warning (lax). It also can warn you once and persist your choice (persistent)

I made these changes for my usecase, but if you like it, here is the pull request. ;)

[sualko]

That is awesome 👏. Thanks a lot. I will merge this as soon as I have time to upgrade this package.