LGTM.com-inspired changes:

- Fix: Ensure all apostrophes are escaped for `toXml` utility
- Fix: Avoid error if `URL` is not defined
- Fix (jPicker): Precision argument had not been passed in previously
- Fix (Star extension): Minor: Avoid erring if `inradius` is `NaN`
- Refactoring: Avoid passing unused arguments, setting unused variables,
  and making unnecessary checks; avoid useless call to `createSVGMatrix`
- Linting (LGTM): Add `lgtm.yml` file (still some remaining items flagged
  but hoping for in-code flagging)
- Docs: Contributing file

editor/extensions/ext-star.js

@@ -170,7 +170,7 @@ export default {
 
             polyPoints += x + ',' + y + ' ';
 
-            if (inradius != null) {
+            if (!isNaN(inradius)) {
               angle = (2.0 * Math.PI * (s / point)) + (Math.PI / point);
               if (orient === 'point') {
                 angle -= (Math.PI / 2);