WIP - a uniform way to assert that a map call was successful

needs review

i don't like that you have to construct the error message before the error occurs.

```
map.rb
+      def expect_map_results(views_touched, msg)
+        compact = views_touched.compact
+        if compact.empty? or compact.member? '<VOID>'
+          screenshot_and_raise msg
+        end
+      end
```

```
+        msg = "could not find view to scroll: '#{uiquery}', args: #{direction}"
+        expect_map_results(views_touched, msg)
```