Explain the tooltips

[GermanCoding]

Postfix TLS logging looks like this:

TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)

And Sendmail like this:

TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO

These log messages, which we display in a HTML title attribute (tooltip), are not entirely self-explanatory. Users might have questions like:

• What does (256/256 bits) mean in Postfix (or Sendmail)?
• What does "cipher" mean?
• What about TLS protocol versions?
• What does Sendmail's verify flag mean?

It would be cool if we had a way to explain these things to users, without completly blowing up the tooltip. At the very least, we need HTML styling to use newlines and perhaps display the data in a more structured form. We could also link to a "help" page which covers these things (may be hosted on Roundcube instances, on a GitHub Wiki, or externally). This also requires some sort of HTML support within the tooltips.

We first need to decide on if and how we want to tackle this and how an implementation could look like. For example, if we wanted to style a custom popup, how do we integrate this with Roundcube themes?

[GermanCoding]

Additional context in #11 (comment)