Improvements to save flow

- Attempt fast save first, only perform conflict resolution if necessary (re: #3056)
- Block reentry of save, and dont keep focus on save button (closes #4641)
- Refactor modeSave() for code clarity (avoid shared state in closure variables)

modules/ui/commit.js

@@ -238,6 +238,7 @@ export function uiCommit(context) {
                 return (n && n.value.length) ? null : true;
             })
             .on('click.save', function() {
+                this.blur();    // avoid keeping focus on the button - #4641
                 dispatch.call('save', this, _changeset);
             });