Tweak details of "Add another tree/resource"

For speedy tree entry, "add another" allows you to just move the marker to a new location. But we don't want that behavior when adding resources. So:
* Call `requireMarkerDrag()` from `addTreeMode.js` rather than from `addMapFeature.js`
* `addResourceMode.js` hides the marker in `initSteps()`
Merge pull request #1305 from RickMohr/add-another

Tweak details of "Add another" tree / resource