Add bold font weight to `wintitle` for HTML output

Fixes #1751
Remove units from zero values to fix lint warnings

Zero values don't need units
Remove redundant border properties

Duplicate properties were set, but last entry (`hidden`) wins by virtue of both order & precedence

See http://www.w3.org/TR/CSS2/tables.html#border-conflict-resolution
In the collapsing border model, `hidden` has the highest priority: if any other conflicting border is set, it won't be displayed.
Merge pull request #1763 from infotexture/feature/bold-wintitle

Bold wintitle in HTML and clean CSS #1751