Update to iD v1.2.0

## 1.2.0

* Don't auto-save intro tutorial edits (#1745, #1795)
* Added waypoint display to GPX layer
* Added "Straighten" operation
* Improve "Orthogonalize" behavior, rename to "Square"
* Add and improve many presets
* Save commit messages on blur (#1783)
* Add KSJ2 tags to discard list (#1794)
* Fix display of labels with wide characters
* Catch localStorage quota exception (#1807)
* Avoid consecutive identical nodes when adding a midpoint (#1296)
* Stop nudge when exiting move mode (#1766)
* Add "Continue" operation
* Delete relations that become empty (#465, #1454)
* Support polygon imagery bounds (#768)
* Pull imagery from editor-imagery-index
* Insert areas in sorted order (#1693)
* Fix some walkthrough glitches (#1744)