Merge gcode processing into one function

Instead of functions for each gcode generator, one function that processes common changes plus specific for each test. Much less code and easier to add future tests.

js/firstlayer.js

@@ -1,4 +1,7 @@
-var originalSquare = `;process Process-1
+var firstlayer = []; 
+
+firstlayer["40_20"] = `
+;process Process-1
 ;layer 1, Z = 0.200
 T0
 G92 E0.0000