Add fallback for non-embedded "Century Gothic" CIDFontType2 font (issue 4722 and bug 879561)

According to practical experiments, falling back to "Arial" when we encounter a non-embedded "[Century Gothic](http://en.wikipedia.org/wiki/Century_Gothic)" `CIDFontType2` font seems to work well.
(Also, the section on Wikipedia about "Printer ink usage" *might* provide some anecdotal evidence that the two fonts are indeed similar.)

Obviously this patch doesn't make "Century Gothic" fonts render perfectly, as is often the case with non-embedded fonts, but all the text is now legible in the referenced issues.

Fixes #4722.
Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=879561.

**Edit:** Both the issues referenced contains files that were exported from SolidWorks.
I'm confused about logic here, if I'm looking at that with lines above: 

```
 // The file data is not specified. Trying to fix the font name
// to be used with the canvas.font.
var fontName = name.replace(/[,_]/g, '-');
var isStandardFont = fontName in stdFontMap;
fontName = stdFontMap[fontName] || nonStdFontMap[fontName] || fontName;
```

Shell we just change: `var isStandardFont = (fontName in stdFontMap) || (fontName in nonStdFontMap);` ?