Completing @alexcjohnson's work started after #3323

• c5d98e6 fixes the range_slider_multiple baseline. It now uses the correct:

// correct - in rangeslider/helpers.js
tickHeight = (ax.side === 'bottom' && ax._boundingBox.height) || 0;

// incorrect - in rangeslider/draw.js
tickHeight = (axisOpts._boundingBox || {}).height || 0;

• I was able to reproduce the jasmine test failure on my laptop. The new range_slider_top_axis mock that @alexcjohnson added fit in the dflt margin.t of 100 on my laptop (and pressumably on CI too). Commit 1a9949d increases the axis title font to ensure the top margin is pushed by the tick labels.