Rename Glyphs custom parameter handler doesn't affect kerning

[simoncozens]

I don't need this in glyphsLib but I discovered in when working on babelfont: The Glyphs "Rename Glyphs" custom parameter also swaps the names of glyphs in the kerning tables as well; we just swap the outlines, meaning the kerning (or lack of kerning) of the old glyph is applied to the new glyph.