Add environment (browser) checks

[blockkeeper]

At startup, check if user has a modern browser environment, block old browsers.

[yeahoffline]

could integrate something like:

https://github.com/kni-labs/old-browsers https://github.com/burocratik/outdated-browser

but i guess our users are mostly mobile or on modern browsers?

[d3ck-org]

They should be :) Cause of our very modern setup and security reasons, I think it makes sense to really block old browsers.