lei_overview: rename {relevance} => {pct}

lei_overview: rename {relevance} => {pct}

The old name was too long compared to the rest of the field
names.  With the Xapian method being named ->get_percent,
"pct" is a well known abbreviation for "percent" and already
used internally by our wrapper.

..And cleanup some excess whitespace while we're in the area.