976058: Fixing problem with titles on tipsy content

There was a problem with the solution to 976058 in that some content already
had tipsy tooltips like on errata  and package searches so we skip adding
titles to those. Also, the row_heights on repository comparison were messed up
so I undid the row height change.
Content Search: Build row and column headers in javascript

Instead of passing html to the javascript from the controller, instead we're
building the html in the javascript. Now the controller is pasing back plain
json which can be more easily escaped.