change date link to something more understandable

change the date link to something human creatable (the uri escapes
got obtuse quickly). Also change it to something which is a valid
css class name so that we could highlight the lines later. This
required some changes to span parsing to inject the additional
css class.

Finally add a couple of fixups suggested by clarkb and fungi on
the last round. This should be ready for main log server.

Change-Id: Ia5111873ee60c174a5c7ddc479fa0c63ead9d97d
Merge "change date link to something more understandable"