Version bit notifications on website

[Sjors]

As of #20 the site sends an email when a version bit is seen (more than VERSION_BITS_THRESHOLD times in the past 100 blocks). We should add an alert to the site itself as well. Something like:

"Version bit BIT was set N times in the past 100 blocks. This could either indicate signalling for an unknown new softfork or miners grinding the block version field."

I can link to BIP 320 for when it's about those bits.

This alert is distinct from monitoring scheduled soft forks in #19.