Swap backspace/delete variant keys

[iankp]

Hello,

I've noticed that the 'delete' and 'backspace' strokes seem to be reversed from what is indicated on emily-modifiers-poster.pdf.

Stroke	Translation on master version	Expected translation
TRA*LTZ	{#delete}	{#backspace}
TRO*LTZ	{#backspace}	{#delete}

The 'A' key generally maps to leftward-moving commands (left, home) and the 'O' key their rightward-moving counterparts. Since backspace erases to the left, it makes sense to associate it with 'A'.

This PR swaps the two translations, so that the output matches the 'expected translation' column above (as well as the poster PDF).

Thanks!