add level parameter to htmlify-screen-log

as an attempt to speed up both logstash, as well as user queries
of the logs, allow for a level parameter, which is the minimum
severity of a log line to display. This filter will work both with
html and text lines, and mean a lot less traffic over the wire.

Also provide links for making it easy to select log levels via
the HTML version of the logs.

Ensure we don't loose non tagged messages by having a "NONE" level
and starting with that when we process logs.

Change-Id: I14a2912d15d25a613c90ef350bcd3a2350456c61
Merge "add level parameter to htmlify-screen-log"